All Geometry Script mesh-writing functions crash on first call in packaged (non-Shipping and Shipping) builds — UE 5.8.3, Windows

General Issues and Bug Reporting (Unreal Engine)
1

Summary

Any Geometry Script function that writes new geometry to a Dynamic Mesh (whether via a Dynamic Mesh Component, Dynamic Mesh Actor, or a bare Dynamic Mesh object created via Construct Object) crashes immediately with an access violation when run in a packaged build. The same Blueprint logic works correctly in-editor (PIE) and in Standalone Game launched from the editor. Functions tested and confirmed crashing: Append Simple Extrude Polygon, Append Box, Append Buffers to Mesh, Add Vertex to Mesh / Add Triangle to Mesh. Functions that do not crash: Reset, Get Num Vertices, mesh query functions, and material assignment.

What Type of Bug are you experiencing?

Framework

Steps to Reproduce

  1. Create a new blank project.
  2. Add a C++ class via Tools > New C++ Class (any class, needed to package at all on 5.8.3 — see note below), build in Visual Studio.
  3. Create a new Actor Blueprint of class Dynamic Mesh Actor.
  4. On Event BeginPlay: Get Dynamic Mesh → Append Box (default parameters).
  5. Place the actor in an Empty Level, set as default map.
  6. Package for Windows (Development or Shipping).
  7. Run the packaged executable.

Expected Result

A box mesh is generated, matching editor/PIE behavior.

Observed Result

Immediate crash on launch (or shortly after, if the call is delayed). Crash signature:

Unhandled Exception: EXCEPTION_ACCESS_VIOLATION reading address 0x0000000000000020
[Callstack] UnrealGame.exe!UObject::execCallMathFunction()
[Callstack] UnrealGame.exe!UObject::execLetObj()
…
[Callstack] UnrealGame.exe!AActor::BeginPlay()

Same failure address (0x20) and callstack shape across every variation tested.

Affects Versions

5.8

Platform(s)

Windows

For crash reports, include your callstack

[2026.10.02-01.38.14:190][ 0]LogWindows: Error: [Callstack] 0x00007ff6a5b907de Test.exe!UObject::execCallMathFunction()
[2026.10.02-01.38.14:190][ 0]LogWindows: Error: [Callstack] 0x00007ff6a5b9284c Test.exe!UObject::execLetObj()
[2026.10.02-01.38.14:190][ 0]LogWindows: Error: [Callstack] 0x00007ff6a5b6de06 Test.exe!ProcessLocalScriptFunction()
[2026.10.02-01.38.14:190][ 0]LogWindows: Error: [Callstack] 0x00007ff6a5b4be16 Test.exe!ProcessScriptFunction<void (__cdecl*)(UObject * __ptr64,FFrame & __ptr64,void * __ptr64)>()
[2026.10.02-01.38.14:190][ 0]LogWindows: Error: [Callstack] 0x00007ff6a5b531fd Test.exe!TThreadSingleton<FDeferredScriptTracker>::Get'::2’::<lambda_1>::operator()()
[2026.10.02-01.38.14:190][ 0]LogWindows: Error: [Callstack] 0x00007ff6a5b6db80 Test.exe!ProcessLocalFunction()
[2026.10.02-01.38.14:190][ 0]LogWindows: Error: [Callstack] 0x00007ff6a5b6de06 Test.exe!ProcessLocalScriptFunction()
[2026.10.02-01.38.14:190][ 0]LogWindows: Error: [Callstack] 0x00007ff6a5b6d601 Test.exe!UObject::ProcessInternal()
[2026.10.02-01.38.14:190][ 0]LogWindows: Error: [Callstack] 0x00007ff6a58bbbf8 Test.exe!UFunction::Invoke()
[2026.10.02-01.38.14:190][ 0]LogWindows: Error: [Callstack] 0x00007ff6a5b6d019 Test.exe!UObject::ProcessEvent()
[2026.10.02-01.38.14:190][ 0]LogWindows: Error: [Callstack] 0x00007ff6a8426377 Test.exe!AActor::ProcessEvent()
[2026.10.02-01.38.14:190][ 0]LogWindows: Error: [Callstack] 0x00007ff6a84043fb Test.exe!AActor::BeginPlay()
[2026.10.02-01.38.14:190][ 0]LogWindows: Error: [Callstack] 0x00007ff6a840b486 Test.exe!AActor::DispatchBeginPlay()
[2026.10.02-01.38.14:190][ 0]LogWindows: Error: [Callstack] 0x00007ff6a9d17049 Test.exe!AWorldSettings::NotifyBeginPlay()
[2026.10.02-01.38.14:190][ 0]LogWindows: Error: [Callstack] 0x00007ff6a8d444b1 Test.exe!AGameStateBase::HandleBeginPlay()
[2026.10.02-01.38.14:190][ 0]LogWindows: Error: [Callstack] 0x00007ff6a9c1560d Test.exe!UWorld::BeginPlay()
[2026.10.02-01.38.14:190][ 0]LogWindows: Error: [Callstack] 0x00007ff6a9d97fcb Test.exe!UEngine::LoadMap()
[2026.10.02-01.38.14:190][ 0]LogWindows: Error: [Callstack] 0x00007ff6a9d58c3f Test.exe!UEngine::Browse()
[2026.10.02-01.38.14:190][ 0]LogWindows: Error: [Callstack] 0x00007ff6a8d6d00b Test.exe!UGameInstance::StartGameInstance()
[2026.10.02-01.38.14:190][ 0]LogWindows: Error: [Callstack] 0x00007ff6a8cedceb Test.exe!UGameEngine::Start()
[2026.10.02-01.38.14:190][ 0]LogWindows: Error: [Callstack] 0x00007ff6ad00e2e3 Test.exe!FEngineLoop::Init()
[2026.10.02-01.38.14:190][ 0]LogWindows: Error: [Callstack] 0x00007ff6ad00d6f7 Test.exe!GuardedMain()
[2026.10.02-01.38.14:190][ 0]LogWindows: Error: [Callstack] 0x00007ff6ad00d8ba Test.exe!GuardedMainWrapper()
[2026.10.02-01.38.14:190][ 0]LogWindows: Error: [Callstack] 0x00007ff6ad0114a0 Test.exe!LaunchWindowsStartup()
[2026.10.02-01.38.14:190][ 0]LogWindows: Error: [Callstack] 0x00007ff6ad020294 Test.exe!WinMain()
[2026.10.02-01.38.14:190][ 0]LogWindows: Error: [Callstack] 0x00007ff6b24804ae Test.exe!__scrt_common_main_seh() [D:\a_work\1\s\src\vctools\crt\vcstartup\src\startup\exe_common.inl:288]
[2026.10.02-01.38.14:190][ 0]LogWindows: Error: [Callstack] 0x00007ff89973cd87 KERNEL32.DLL!UnknownFunction

Additional Notes

  • The crash is deterministic, not timing-related — reproduced with delays from 0 to 10 seconds before the call.
  • No debug symbols were available in any crash dump despite enabling “Include Debug Files” in packaging settings; the .pdb was present but the engine’s own crash reporter did not resolve symbols from it.
  • A separate issue was also encountered on 5.8.3: pure Blueprint-only projects fail to package at all with a Turnkey/BuildTargetInfo ensure error, requiring an empty C++ class to be added as a workaround. This may or may not be related to the main issue.
  • Engine installation was verified via the Epic Games Launcher with no changes reported.