"UniformBufferRHI" Random Crash

Development Rendering
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1

Engine version is 4.24.3. I’ve been intermittently getting crashes with the following crash report:

Assertion failed: UniformBufferRHI.GetReference() [File:D:\Build\++UE4\Sync\Engine\Source\Runtime\RenderCore\Public\UniformBuffer.h] [Line: 87] Attempted to access UniformBufferRHI on a TUniformBuffer that was never filled in with anything

And here’s the callstack from the logs:

[2020.07.08-20.39.42:502][829]LogWindows: Windows GetLastError: The operation completed successfully. (0)
[2020.07.08-20.39.42:503][829]LogWindows: Error: === Critical error: ===
[2020.07.08-20.39.42:503][829]LogWindows: Error: 
[2020.07.08-20.39.42:503][829]LogWindows: Error: Fatal error: [File:U:\UE_4.25_Source\Engine\Source\Runtime\RenderCore\Private\RenderingThread.cpp] [Line: 855] 
[2020.07.08-20.39.42:503][829]LogWindows: Error: Rendering thread exception:
[2020.07.08-20.39.42:503][829]LogWindows: Error: Fatal error: [File:U:\UE_4.25_Source\Engine\Source\Runtime\Engine\Private\SceneManagement.cpp] [Line: 1131] 
[2020.07.08-20.39.42:503][829]LogWindows: Error: FMeshBatch was not properly setup. No primitive uniform buffer was specified and the vertex factory does not have a valid primitive id stream.
[2020.07.08-20.39.42:503][829]LogWindows: Error: 	VertexFactory[Name: FMeshParticleVertexFactory, Initialized: 1]
[2020.07.08-20.39.42:503][829]LogWindows: Error: 	PrimitiveSceneProxy[Level: /Game/Maps/PrototypeMap/UEDPIE_2_PrototypeMap, Owner: MGBulletProjectile_C_72, Resource: PS_ShotgunAndSMG_Projectile]
[2020.07.08-20.39.42:503][829]LogWindows: Error: 
[2020.07.08-20.39.42:503][829]LogWindows: Error: 
[2020.07.08-20.39.42:503][829]LogWindows: Error: [Callstack] 0x00007ffd9882a799 KERNELBASE.dll!UnknownFunction []
[2020.07.08-20.39.42:503][829]LogWindows: Error: [Callstack] 0x00007ffd5aeff0f6 UE4Editor-Core.dll!ReportAssert() [U:\UE_4.25_Source\Engine\Source\Runtime\Core\Private\Windows\WindowsPlatformCrashContext.cpp:1537]
[2020.07.08-20.39.42:503][829]LogWindows: Error: [Callstack] 0x00007ffd5aefb848 UE4Editor-Core.dll!FWindowsErrorOutputDevice::Serialize() [U:\UE_4.25_Source\Engine\Source\Runtime\Core\Private\Windows\WindowsErrorOutputDevice.cpp:78]
[2020.07.08-20.39.42:503][829]LogWindows: Error: [Callstack] 0x00007ffd5ac8ec4d UE4Editor-Core.dll!FOutputDevice::LogfImpl() [U:\UE_4.25_Source\Engine\Source\Runtime\Core\Private\Misc\OutputDevice.cpp:61]
[2020.07.08-20.39.42:503][829]LogWindows: Error: [Callstack] 0x00007ffd5865c288 UE4Editor-Engine.dll!FMeshBatch::PreparePrimitiveUniformBuffer() [U:\UE_4.25_Source\Engine\Source\Runtime\Engine\Private\SceneManagement.cpp:1123]
[2020.07.08-20.39.42:503][829]LogWindows: Error: [Callstack] 0x00007ffd586589e0 UE4Editor-Engine.dll!FMeshElementCollector::AddMesh() [U:\UE_4.25_Source\Engine\Source\Runtime\Engine\Private\SceneManagement.cpp:268]
[2020.07.08-20.39.42:503][829]LogWindows: Error: [Callstack] 0x00007ffd57cfcb16 UE4Editor-Engine.dll!FDynamicMeshEmitterData::GetDynamicMeshElementsEmitter() [U:\UE_4.25_Source\Engine\Source\Runtime\Engine\Private\Particles\ParticleSystemRender.cpp:1837]
[2020.07.08-20.39.42:503][829]LogWindows: Error: [Callstack] 0x00007ffd57cf9dfa UE4Editor-Engine.dll!FParticleSystemSceneProxy::GetDynamicMeshElements() [U:\UE_4.25_Source\Engine\Source\Runtime\Engine\Private\Particles\ParticleSystemRender.cpp:6934]
[2020.07.08-20.39.42:503][829]LogWindows: Error: [Callstack] 0x00007ffd49c4f248 UE4Editor-Renderer.dll!FSceneRenderer::GatherDynamicMeshElements() [U:\UE_4.25_Source\Engine\Source\Runtime\Renderer\Private\SceneVisibility.cpp:2918]
[2020.07.08-20.39.42:503][829]LogWindows: Error: [Callstack] 0x00007ffd49c4a8cc UE4Editor-Renderer.dll!FSceneRenderer::ComputeViewVisibility() [U:\UE_4.25_Source\Engine\Source\Runtime\Renderer\Private\SceneVisibility.cpp:4006]
[2020.07.08-20.39.42:503][829]LogWindows: Error: [Callstack] 0x00007ffd49c50577 UE4Editor-Renderer.dll!FDeferredShadingSceneRenderer::InitViews() [U:\UE_4.25_Source\Engine\Source\Runtime\Renderer\Private\SceneVisibility.cpp:4305]
[2020.07.08-20.39.42:503][829]LogWindows: Error: [Callstack] 0x00007ffd499122eb UE4Editor-Renderer.dll!FDeferredShadingSceneRenderer::Render() [U:\UE_4.25_Source\Engine\Source\Runtime\Renderer\Private\DeferredShadingRenderer.cpp:1376]
[2020.07.08-20.39.42:503][829]LogWindows: Error: [Callstack] 0x00007ffd49c20951 UE4Editor-Renderer.dll!RenderViewFamily_RenderThread() [U:\UE_4.25_Source\Engine\Source\Runtime\Renderer\Private\SceneRendering.cpp:3581]
[2020.07.08-20.39.42:503][829]LogWindows: Error: [Callstack] 0x00007ffd49c169b8 UE4Editor-Renderer.dll!TEnqueueUniqueRenderCommandType<`FRendererModule::BeginRenderingViewFamily'::`35'::FDrawSceneCommandName,<lambda_4495dfbf235452f2a02310cb16370cef> >::DoTask() [U:\UE_4.25_Source\Engine\Source\Runtime\RenderCore\Public\RenderingThread.h:195]
[2020.07.08-20.39.42:503][829]LogWindows: Error: [Callstack] 0x00007ffd49c1751d UE4Editor-Renderer.dll!TGraphTask<TEnqueueUniqueRenderCommandType<`FRendererModule::BeginRenderingViewFamily'::`35'::FDrawSceneCommandName,<lambda_4495dfbf235452f2a02310cb16370cef> > >::ExecuteTask() [U:\UE_4.25_Source\Engine\Source\Runtime\Core\Public\Async\TaskGraphInterfaces.h:849]
[2020.07.08-20.39.42:503][829]LogWindows: Error: [Callstack] 0x00007ffd5aa1147f UE4Editor-Core.dll!FNamedTaskThread::ProcessTasksNamedThread() [U:\UE_4.25_Source\Engine\Source\Runtime\Core\Private\Async\TaskGraph.cpp:692]
[2020.07.08-20.39.42:503][829]LogWindows: Error: [Callstack] 0x00007ffd5aa11823 UE4Editor-Core.dll!FNamedTaskThread::ProcessTasksUntilQuit() [U:\UE_4.25_Source\Engine\Source\Runtime\Core\Private\Async\TaskGraph.cpp:587]
[2020.07.08-20.39.42:503][829]LogWindows: Error: [Callstack] 0x00007ffd7ae5e352 UE4Editor-RenderCore.dll!RenderingThreadMain() [U:\UE_4.25_Source\Engine\Source\Runtime\RenderCore\Private\RenderingThread.cpp:341]
[2020.07.08-20.39.42:503][829]LogWindows: Error: [Callstack] 0x00007ffd7ae5e794 UE4Editor-RenderCore.dll!FRenderingThread::Run() [U:\UE_4.25_Source\Engine\Source\Runtime\RenderCore\Private\RenderingThread.cpp:473]
[2020.07.08-20.39.42:503][829]LogWindows: Error: [Callstack] 0x00007ffd5af1e37b UE4Editor-Core.dll!FRunnableThreadWin::Run() [U:\UE_4.25_Source\Engine\Source\Runtime\Core\Private\Windows\WindowsRunnableThread.cpp:86]
[2020.07.08-20.39.42:503][829]LogWindows: Error: [Callstack] 0x00007ffd5af1e1f4 UE4Editor-Core.dll!
[2020.07.08-20.39.42:503][829]LogWindows: Error: 
[2020.07.08-20.39.42:503][829]LogWindows: Error: 
[2020.07.08-20.39.42:520][829]LogExit: Executing StaticShutdownAfterError
[2020.07.08-20.39.42:525][829]LogWindows: FPlatformMisc::RequestExit(1)
[2020.07.08-20.39.42:525][829]LogCore: Engine exit requested (reason: Win RequestExit)
[2020.07.08-20.39.42:533][829]Log file closed, 07/08/20 14:39:42

I’ve never seen this error prior to 4.24. It happens most often while spawning particle systems, like projectile particles for my weapons. But it’s so intermittent that I have no idea what could be causing it… sometimes I can test play for half an hour, other times it happens after I’ve fired two bullets. Still other times it appears to happen when I spawn emitters for other effects.

Any ideas? Thanks!

2

After weeks of troubleshooting, modifying source code, and painstakingly trying to isolate anything I could possibly think of, I might be slightly closer to finding the problem. My observations so far…

→ The crash only seems to occur, or at least happens more quickly, when I’m playing with multiple clients (as opposed to a Listen Server and a client or just one client).

→ I tried out using different particles to see if it would stop the crash. I found one from a Marketplace content called “Action FX Pack.” The particle is called “Fire_Bullet,” and if I use it out-of-the-box with no changes, the crash seems to stop happening. However, if I start turning off certain emitters, the crash starts happening again.

I’m still working out which emitters exactly are causing the crash when I turn them off. It’s extremely odd to me that turning off emitters would cause this, but literally that’s the only difference between getting this crash and not at the moment…

3

Oh dear… well, I found the problem. My comment is irrelevant now, turns out I was treating symptoms rather than the root cause. A few months ago, I switched over to my Desktop computer to do the majority of the game work. One of the first things I did at that time was to set the Project Settings frame rate to be “Fixed” at 60, because I was getting over 100FPS on Desktop and I didn’t want that, so it seemed like a natural thing to do.

That’s what broke it. And of course because I use source control, everything carried over to my laptop, so I couldn’t isolate it that way which made it even more confusing. Setting to a Smooth Frame Rate with a range max of 60 has completely stopped the crashing.

I never want to look at or think about this again… but I’ve made a personal note to start tracking these kinds of global changes when I make them, because they’ll get you every time. I hope this helps someone with a similar problem in the future avoid any unnecessary stress!