5.8.1 Hotfix Released

General Announcements
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We’ve got hotfix 5.8.1 coming your way with over 260 fixes and updates!

Please feel free to share feedback and discuss the current version in the release topic, Unreal Engine 5.8 Released.

If you experience a bug with the 5.8.1 Hotfix, please follow the How to Report a Bug guide to report it on the Bug Submission Form.

UE 5.8.1 Release Notes

  • AI/ML

    • MCP (Bug Fix)

      • Avoid fatal crashes when adding a component to a Blueprint with no SimpleConstructionScript.

      • [ModelContextProtocol][HTTPServer] Fix tools/call response framing for both progress and non-progress paths.

      • Disable transactions during tool script execution

  • Animation

    • Animating in Engine (Bug Fix)

      • Fixed: [Animator Kit] fix mesh normal flickering artifacts when using Deformer Rigs on certain meshes

    • IK & Retargeting (Bug Fix)

      • Fixed a critical issue with JSON import not creating RigMapper Definition editor graph.

      • Fix for check failure due to non-normalized local space rotations

    • Sequencer (New)

      • Sequencer: Anim Mixer: Filter bus name suggestions per-character in bus target/section UI

    • Sequencer (Bug Fix)

      • Sequencer: Fixed undo failing to restore all keys when deleting keys across multiple tracks

      • Sequencer: Anim Mixer: Fix ‘Gap Behavior’ not updating after changing it.

      • Sequencer: Anim Mixer bone matching: fix the rotation offset for non-root match bones.

      • Sequencer: Anim Mixer: fix muting/unmuting a track or spawnable corrupts bone matching

      • Sequencer: Anim Mixer: Fix mixer sections collapsing to the reference pose (bone matching also fails) when a second mixer drives the same skeletal mesh.

      • Sequencer: Anim Mixer: Fix crash on LOD change while drawing skeletons.

      • Sequencer: Fixed a regression that broke editing time warp curves in the Curve Editor

      • Sequencer: Anim Mixer - fix duplicated/copied bindings sharing Control Rig child tracks.

      • Sequencer: Anim Mixer: Fix crash on LOD change while drawing skeletons.

      • Sequencer: Anim Mixer: Fix root motion extracted without root motion settings in Anim Mixer

      • Sequencer: Fixed an crash when splitting an animation Mask Section in Sequencer, caused by SplitSection assuming a section’s owner is always a track rather than a section-provider decoration.

      • Sequencer: Guard null AddInteraction result in FSequencerEdMode::Enter

      • Sequencer: Fix crash reopening a Level Sequence with an Anim Mixer “DefaultTarget” after editor restart

      • Sequencer: Fix crash opening a level sequence with a Stitch Section after editor restart

      • Sequencer: Fix crash when a Keep State section overlaps a Restore State section

    • Skeletal Editing (Bug Fix)

      • Fixed [Skeletal Mesh Editor]: fix a crash in Edit Skin Weight tool when committing one bone’s skin weight by clicking on another bone’s slider in the “Mesh” mode when directly editing skin weights of selected mesh elements

  • Editor

    • Editor (Bug Fix)

      • LiveCoding: Fix possible crash on editor shutdown

      • Fixed a crash that could happen when typing in the search field of a menu while scrolling with the mouse in a submenu.

      • [EditorTRSGizmo] Only send InputWidgetDelta messages when the incoming delta is not (nearly) zero.

      • [EditorTRSGizmo] Hide the old location for the combined gizmo. Force off the new gizmos when enabling the combined gizmo. Force off the combined gizmo when enabling the new gizmos.

      • [EditorTRSGizmo] Add ClampMax values to several user-exposed visual style values.

      • [Viewport] Don’t release mouse capture when the middle mouse button is held.

    • Interchange (Bug Fix)

      • Fix MaterialX primvar baking system producing incorrect results for some specific scenes when importing referenced MaterialX materials via Interchange USD

    • UI (Bug Fix)

      • Editor: Fixed save-asset dialogs (Duplicate Asset, LiveLink, MRQ, PCG, etc.) ignoring the caller-supplied DefaultPath and always defaulting to /Game, so duplicated assets now save to the intended folder.

      • Correction to a hang that may happen in Unreal Editor when the user clicks in the Text Box.

  • Framework

    • Blueprint Compiler (Bug Fix)

      • Fixed one cause of reentrant blueprint compilation

  • Level Design and Art Tools

    • Geometry Core (Bug Fix)

      • Fixed an issue where the UV Packer could crash or ensure if given an invalid texture resolution.

    • Landscape (Bug Fix)

      • Fixed crash when landscape editor mode is exited after the application is shutdown

      • Made landscape editor tools use legacy viewport interactions. This fixes landscape spline tangent manipulation that had regressed in 5.8

      • Fixed ensure when creating a template UTexture (this can happen when copy-pasting)

    • Modeling Tools (Bug Fix)

      • Fixed editor crash that could happen with mesh partition, by more consistently guarding against null MeshComponents entries in ACompiledSection and APreviewSection

      • Fixed a crash that could occur with mesh terrain sculpt layer UI in the sculpt tools.

      • Fixed modeling mode tools not starting in some cases for static meshes attached under a BP or other separate actor.

    • Procedural (Bug Fix)

      • [PCG] Fix Max Shader Feature Level Switch not activating SM5 pin when previewing Mac Metal SM5.

      • Prevent crashes due to unnormalized rotations, in spawners and combine points nodes.

      • [PCG] Fix default point seed value written by Point Generator nodes getting set to 0 instead of 42.

      • Fixed indexing error in the Duplicate Point node when more than 64 points were duplicated. Could lead to some crashes in the editor.

      • Fixed potential editor crash when double clicking a point in the attribute list view with an invalid rotation.

      • Fixed deprecation problem with generation radii and higen grid cell exponential. Radii were not properly multiplied. This was causing an issue in the Cassini Sample project.

    • World Building (Bug Fix)

      • Limited name length for dynamic pin renaming - i.e. Python Data Processor

  • Media

    • Media (Bug Fix)

      • TMV Pipeline optimizations

      • Render thread performance: texture vs struct buffer: Using Struct Buffer with upload heap allows to move the cost of buffer copy from cpu (render thread) to the gpu.

      • Memory usage (sparse output and buffer virtualization): reduces overall needed memory for 16K videos, clamping to memory budgets through tile buffer virtualization and sharing.

      • Fix Electra H.264/H.265 decoder factories rejecting 4K portrait-orientation video

      • Fix a performance regression in game builds caused by media textures walking all material instances on texture resize. This is now disabled in game builds, returning to pre-5.8 functionality. Targeted use case are editor only for now.

  • MetaHuman

    • MetaHuman (New)

      • Gates MetaHumanGenerator toolset registration on optional content availability

      • MetaHumanGenerator.h/.cpp: wraps dependency check

      • init_unreal.py: extend the existing conditional registration to also require is_optional_content_installed(); otherwise log a warning and skip register_toolset_class.

      • Reproduced crash: with the optional folder removed, set_skin_tone calls reliably triggers the assert to crash UE.

      • Verified fix: without optional folder now toolset does not register.

      • With optional content folder toolset continues to work as intended.

    • MetaHuman (Bug Fix)

      • Fixed a crash in MetaHuman Creator that can happen when clothing and hair assets have been renamed

      • [MetaHuman Manager] The sub-item exclusion UI is now in a scrollable view.

      • [MetaHuman Manager] Multi-selection involving MetaHuman Assemblies is not allowed.

      • Restore legacy UEMHC compatibility of DNA state when MetaHuman assets are reloaded

      • Fix crash in MetaHuman Animator which occurs if Unreal Engine is installed to path containing non ASCII characters.

      • [MHCrowd] Overrides teleport handling for MetaHuman Crowd actors so the Mover plugin’s authoritative simulation state is updated alongside the actor transform. This prevents pooled actors reused for new entities from snapping back to the previous occupant’s stale position when driven in Walking mode.

      • Fix generating SkeletalMeshes from DNA assets that went through a round-trip through external tools

      • Fix DNA asset reimport not marking the package as dirty

      • Force conversion to the canonical UEMHC source coordinate system on all entry points where DNAs are fed into UEMHC

      • Fixed an issue where promoted frames displayed tracking markers misaligned with the face when using footage with a higher-rate image sequence (for example, 60fps) paired with a lower-rate depth sequence (for example, 30fps). Frames past the halfway point of the clip were affected.

      • Fix DNA twist axis remapping for a subset of possible to/from coordinate spaces during coordinate system conversion

      • Force all DNA exports from UEMHC into the canonical source coordinate system, while normal right click → Export DNA option will honor the current coordinate system always

      • Add import dialog during DNA drag and drop into content browser to choose target coordinate system (UE Default / MetaHuman compatible options)

      • [UEMHC] Always export eyelashes mask in DCC export, even when selection is None

      • Changed GetEyelashesMask to take EMetaHumanCharacterEyelashesType instead of FMetaHumanCharacterEyelashesProperties

      • In ExportUnmodifiedTextures, fall back to ShortSparse when eyelashes type is None so an eyelashes mask is always exported

      • Added precondition checks in ExportCharacterForDCC to fail early if the character is not rigged or lacks high resolution textures

      • Added character object token to all error message logs in ExportCharacterForDCC

      • Added MetaHumanCharacterDCCExportTests.cpp with unit tests for GetEyelashesMask and integration tests for the DCC export pipeline

      • Move MakeTDSScopedExchangeCodeHandler into a shared UE::MetaHuman::TestUtils namespace

      • Also fix Export preconditions to ensure error messages are captured in the test

      • Fix Editor crash if a user upgrades an old asset to the new DNA by reimporting DNA through SkeletalMesh, and then tries setting the Legacy DNA back as asset user data on the SkeletalMesh

  • Mobile Rendering

    • Mobile Lighting (Bug Fix)

      • Fix mobile bloom pyramid step factor independently from the quality factor

  • Movie Render Pipeline

    • Movie Render Pipeline (Bug Fix)

      • Fixed an issue in MRG that caused the Accumulation DOF effect to appear broken if “Enable Motion Blur” was enabled on the Accumulation DOF component.

  • Platform

    • All Apple (Bug Fix)

      • Fix crashes in breadcrumb Begin/End on Metal.

      • Fix bug with MSC entrypoints being renamed when compiling libs, this caused the runtime name to differ from the name in the metallib.

      • Fixed bug with DXC reflection returning incorrect size for float4x4 and hitting ensure in MeshDrawShaderBindings.

    • Windows (New)

      • Add support for NVidia ARM64 libraries for when they are released:

      • Engine/Source/ThirdParty/NVIDIA/nvapi/aarch64/nvapia64.lib

      • Engine/Source/ThirdParty/NVIDIA/NVaftermath/lib/arm64/GFSDK_Aftermath_Lib.arm64.lib

      • Engine/Binaries/ThirdParty/NVIDIA/NVaftermath/Win64/GFSDK_Aftermath_Lib.arm64.dll

  • Platform Mobile

    • iOS, tvOS, and iPadOS (Bug Fix)

      • Fix libogg path for visionOS

      • [PLCrashReporter]

      • [Ogg]

      • Add missing go-ios app for launching iOS Remote Mac builds under Windows

  • Rendering

    • Lighting (Bug Fix)

      • [VSM] Fixed issue where primitives with forced static invalidation behavior are still put in the dynamic shadow map slice if World Position Offset is enabled.

    • Materials and Shaders (Bug Fix)

      • Crash Fix:

      • Fixed a 1-byte null terminator stomp in shader preprocessor copy loops; removed the padding hack that was added to work around a 100% crash on Mac platforms that was caused by this stomp. Note that this was also causing rare crashes on shader preprocessing on Windows but much more rarely due to differences in allocator behaviour.

      • Crash Fix:

      • Hooked up shader preprocessor asserts to engine check mechanism; these were previously being compiled out and so ignored. Added new asserts to harden against null/short source buffers reaching copy_to_action_point.

    • Nanite (Bug Fix)

      • Fix GPU crash in Nanite Voxel rasterizer.

    • Postprocessing (Bug Fix)

      • [TSR] Enable TSR 16bit VALU for Nvidia driver newer than 610.00 by default as a compiler bug has been fixed and it has better performance.

      • [GTAO] Fix crash due to Scene Velocity not generated with a safe produced guard.

      • [TSR] Fix incorrect TSR Thin geometry relaxation weight when has pixel animation bit is set for edge detection.

    • RHI (Bug Fix)

      • Fix deadlocks and crashes when RHI parallel translation is turned off.

      • D3D12 residency: gate CREATE_NOT_RESIDENT on ID3D12Device8 (Win10 20H1+)

  • Simulation

    • Cloth (New)

      • Chaos Cloth - Cached the p.ClothPhysics.UseEndTickWait CVar pointer to avoid a per-tick FindConsoleObject lookup.

    • Cloth (Bug Fix)

      • Chaos Cloth - Fixed constraint space rotations that got broken in 5.8.0.

      • [Chaos Cloth] Apply skeleton root bone scale to simulation colliders.

      • [Chaos Cloth Asset] Fixed crash when reloading a USD sim mesh that defines fabrics

      • Chaos Cloth Asset - Restored the bSimulateInEditor PostEditChangeProperty branch.

      • Chaos Cloth - Fixed DrawLocalSpace, DrawVelocityScale and DrawPointNormals debug visualizations.

      • Chaos Cloth/Outfit Asset - Fixed old cloth and outfit asset rendering being culled by stale serialised bounds.

      • Chaos SKM Cloth Asset - Fixed collision bone orientations when using the SKM Clothing Data integration.

    • Core Physics (Bug Fix)

      • Chaos: Fix NaN/Inf in USkeletalMeshComponent::UpdateRigidBodyScaling when scaling to zero and back

    • Dataflow (Bug Fix)

      • Fixed crash on fractures with small collision sample spacing

      • Dataflow : Fixed “Select By Primitive” node not working properly when outputting face selection type

      • Dataflow Editor : Fixed Geometry Collection and Cloth Collection renderable types not properly rendering color attributes

      • Dataflow Editor : Fixed Weight-map Tool to properly hide rendered component after a Cancel or Accept event so that the painted mesh is no longer hidden under it

      • Dataflow Editor : Fixed issues related to embedding a Dataflow graph into an asset

      • Dataflow : Made logic more robust when deciding to transfer existing painted maps onto input collections with a different topology

    • General Physics (Bug Fix)

      • Fixed crashes happening when using Cluster Merge on a Geometry collection with a single bone

  • UI

    • Slate (Bug Fix)

      • Fix to a crash in Slate MultiBox when using Toolbars in Unreal Editor

      • Fixed crash in Slate when instanced stereo or VR was enabled with kawase blur.

      • Fixed issue with FTextInputMethodContext where the Korean IME (and potentially others) would be unable to insert characters after a line break

  • Virtual Production

    • Virtual Production (Bug Fix)

      • Fixed issue where attempting to capture a media texture using a file media output with ‘Invert Alpha’ unchecked would result in blank images.

    • Performance Capture (Bug Fix)

      • [Performance Capture Workflow] - Fix crash on hot reload entering and exiting a sandbox session with a PCap UMG viewport tab open. Fix is introduced by using the spawn tab by class, rather than by object.

      • OBS LiveLink Device: Fixed overwriting OBS Studio side FilenameFormatting profile setting

    • Tools (Bug Fix)

      • Fixed issue where baking animation from a sub-sequence would incorrectly fail when initiated from a sequence opened with the Take Recorders “Review Last Recording” button.

  • AI/ML

    • MCP (Upgrade Notes)

      • Fixed a crash that could occur when having the Assistant edit certain kinds of Blueprints.

      • Changes made by the Assistant during a script execution are no longer bundled together in a single transaction.

  • MetaHuman

    • MetaHuman (Upgrade Notes)

      • If the main BP for a MHCrowd Actor was copied from the original sample and has a section labeled “Update mover component for new character location”, this section can now be deleted.

  • Platform

    • Windows (Upgrade Notes)

      • When the Windows ARM64 native NVidia libraries for NVAPI and NVAftermath are released, they must be manually copied to the relevant locations.

  • Platform Mobile

    • iOS, tvOS, and iPadOS (Upgrade Notes)

      • Due to a path issue in 5.8.0, you may have to manually change an iOS specific library path if you get a libCrashReporter linker error with a Remote Mac iOS build. Change the installed library path from: “Engine\Source\ThirdParty\PLCrashReporter\lib\lib-Xcode-16.2\IOS\Release” to "Engine\Source\ThirdParty\PLCrashReporter\lib\lib-Xcode-16.2\iOS\Release. Note the change in case of the “ios” path component from “IOS” to “iOS”

      • Due to a path issue in 5.8.0, you may have to manually change an iOS specific library path if you get a libogg linker error with a Remote Mac iOS build. Change the installed library path from: “Engine\Source\ThirdParty\Ogg\libogg-1.2.2\lib\IOS” to “Engine\Source\ThirdParty\Ogg\libogg-1.2.2\lib\ios”. Note the change in case of the last path component.