I’m encountering an issue when creating an actor blueprint using Mutable’s CustomizableSkeletal.
When I apply a Niagara system to the actor with an emitter that uses the Initialize Mesh Reproduction Sprite and/or Update Mesh Reproduction Sprite modules, it often causes an engine crash. In some cases, the engine doesn’t crash, but the effect fails to display.
The crash behavior is somewhat erratic. Recompiling the Mutable object, the actor blueprint, or restarting the editor typically causes the bug to resurface.
I tested this in the Third Person Template, and it happens quite reliably. When I follow the same steps in a project compiled from C++, I hit a breakpoint when the exception is raised. However, if I continue execution, the effect displays correctly, and no other issues occur.
I’ve been experimenting with different configurations in both Mutable and Niagara to find a workaround, but so far, nothing has worked. I haven’t found any other posts or issues describing this problem, but it seems fairly easy to reproduce.
I’ve already reported the bug, but I’d love to know if you have any workaround to get it working as is.
I also have video evidence, but for some reason when I try to upload it on this question the upload gets stuck on 100% forever.
This is the log file for the crash:
[2025.06.13-13.15.51:526][736]LogThreadingWindows: Error: Runnable thread Foreground Worker #1 crashed.
[2025.06.13-13.15.51:528][736]LogWindows: Error: === Critical error: ===
[2025.06.13-13.15.51:528][736]LogWindows: Error:
[2025.06.13-13.15.51:528][736]LogWindows: Error: Assertion failed: (Index >= 0) & (Index < ArrayNum) [File:D:\build\++UE5\Sync\Engine\Source\Runtime\Core\Public\Containers\Array.h] [Line: 1067]
[2025.06.13-13.15.51:528][736]LogWindows: Error: Array index out of bounds: 0 into an array of size 0
[2025.06.13-13.15.51:528][736]LogWindows: Error:
[2025.06.13-13.15.51:528][736]LogWindows: Error:
[2025.06.13-13.15.51:528][736]LogWindows: Error: [Callstack] 0x00007fffccd04018 UnrealEditor-Core.dll!FDebug::CheckVerifyFailedImpl2() [D:\build\++UE5\Sync\Engine\Source\Runtime\Core\Private\Misc\AssertionMacros.cpp:728]
[2025.06.13-13.15.51:528][736]LogWindows: Error: [Callstack] 0x00007fff9e3bebcd UnrealEditor-Niagara.dll!TAreaWeightingModeBinder<TUNiagaraDataInterfaceSkeletalMesh_RandomTriCoordBinder>::Bind<TIntegralConstant<ENDISkeletalMesh_FilterMode,0> >() [D:\build\++UE5\Sync\Engine\Plugins\FX\Niagara\Source\Niagara\Classes\NDISkeletalMeshCommon.h:586]
[2025.06.13-13.15.51:528][736]LogWindows: Error: [Callstack] 0x00007fff9e4cf0fe UnrealEditor-Niagara.dll!UNiagaraDataInterfaceSkeletalMesh::BindTriangleSamplingFunction() [D:\build\++UE5\Sync\Engine\Plugins\FX\Niagara\Source\Niagara\Private\NDISkeletalMesh_TriangleSampling.cpp:358]
[2025.06.13-13.15.51:528][736]LogWindows: Error: [Callstack] 0x00007fff9e8d2b15 UnrealEditor-Niagara.dll!UNiagaraDataInterfaceSkeletalMesh::GetVMExternalFunction() [D:\build\++UE5\Sync\Engine\Plugins\FX\Niagara\Source\Niagara\Private\NiagaraDataInterfaceSkeletalMesh.cpp:2459]
[2025.06.13-13.15.51:528][736]LogWindows: Error: [Callstack] 0x00007fff9ebae931 UnrealEditor-Niagara.dll!FNiagaraScriptExecutionContext::Tick() [D:\build\++UE5\Sync\Engine\Plugins\FX\Niagara\Source\Niagara\Private\NiagaraScriptExecutionContext.cpp:394]
[2025.06.13-13.15.51:528][736]LogWindows: Error: [Callstack] 0x00007fff9e9a546f UnrealEditor-Niagara.dll!FNiagaraEmitterInstanceImpl::PreTick() [D:\build\++UE5\Sync\Engine\Plugins\FX\Niagara\Source\Niagara\Private\NiagaraEmitterInstanceImpl.cpp:1078]
[2025.06.13-13.15.51:528][736]LogWindows: Error: [Callstack] 0x00007fff9ec37819 UnrealEditor-Niagara.dll!FNiagaraSystemInstance::Tick_Concurrent() [D:\build\++UE5\Sync\Engine\Plugins\FX\Niagara\Source\Niagara\Private\NiagaraSystemInstance.cpp:2689]
[2025.06.13-13.15.51:528][736]LogWindows: Error: [Callstack] 0x00007fff9ebfb5f5 UnrealEditor-Niagara.dll!FNiagaraSystemSimulation::FlushTickBatch() [D:\build\++UE5\Sync\Engine\Plugins\FX\Niagara\Source\Niagara\Private\NiagaraSystemSimulation.cpp:1051]
[2025.06.13-13.15.51:528][736]LogWindows: Error: [Callstack] 0x00007fff9ebdd06d UnrealEditor-Niagara.dll!FNiagaraSystemSimulation::AddSystemToTickBatch() [D:\build\++UE5\Sync\Engine\Plugins\FX\Niagara\Source\Niagara\Private\NiagaraSystemSimulation.cpp:1027]
[2025.06.13-13.15.51:528][736]LogWindows: Error: [Callstack] 0x00007fff9ec39ef6 UnrealEditor-Niagara.dll!FNiagaraSystemSimulation::Tick_Concurrent() [D:\build\++UE5\Sync\Engine\Plugins\FX\Niagara\Source\Niagara\Private\NiagaraSystemSimulation.cpp:1848]
[2025.06.13-13.15.51:528][736]LogWindows: Error: [Callstack] 0x00007fff9ebf32b4 UnrealEditor-Niagara.dll!TGraphTask<FNiagaraSystemSimulationTickConcurrentTask>::ExecuteTask() [D:\build\++UE5\Sync\Engine\Source\Runtime\Core\Public\Async\TaskGraphInterfaces.h:706]
[2025.06.13-13.15.51:528][736]LogWindows: Error: [Callstack] 0x00007fff9e2b4c40 UnrealEditor-Niagara.dll!UE::Tasks::Private::FTaskBase::TryExecuteTask() [D:\build\++UE5\Sync\Engine\Source\Runtime\Core\Public\Tasks\TaskPrivate.h:527]
[2025.06.13-13.15.51:528][736]LogWindows: Error: [Callstack] 0x00007fff9e222244 UnrealEditor-Niagara.dll!LowLevelTasks::TTaskDelegate<LowLevelTasks::FTask * __ptr64 __cdecl(bool),48>::TTaskDelegateImpl<`LowLevelTasks::FTask::Init<`UE::Tasks::Private::FTaskBase::Init'::`2'::<lambda_1> >'::`13'::<lambda_1>,0>::CallAndMove() [D:\build\++UE5\Sync\Engine\Source\Runtime\Core\Public\Async\Fundamental\TaskDelegate.h:171]
[2025.06.13-13.15.51:528][736]LogWindows: Error: [Callstack] 0x00007fffcc9cdc55 UnrealEditor-Core.dll!LowLevelTasks::FTask::ExecuteTask() [D:\build\++UE5\Sync\Engine\Source\Runtime\Core\Public\Async\Fundamental\Task.h:627]
[2025.06.13-13.15.51:528][736]LogWindows: Error: [Callstack] 0x00007fffcc9cd9b6 UnrealEditor-Core.dll!LowLevelTasks::FScheduler::ExecuteTask() [D:\build\++UE5\Sync\Engine\Source\Runtime\Core\Private\Async\Fundamental\Scheduler.cpp:365]
[2025.06.13-13.15.51:528][736]LogWindows: Error: [Callstack] 0x00007fffcc9f3d11 UnrealEditor-Core.dll!LowLevelTasks::FScheduler::WorkerLoop() [D:\build\++UE5\Sync\Engine\Source\Runtime\Core\Private\Async\Fundamental\Scheduler.cpp:724]
[2025.06.13-13.15.51:528][736]LogWindows: Error: [Callstack] 0x00007fffcc9b5fe5 UnrealEditor-Core.dll!`LowLevelTasks::FScheduler::CreateWorker'::`2'::<lambda_1>::operator()() [D:\build\++UE5\Sync\Engine\Source\Runtime\Core\Private\Async\Fundamental\Scheduler.cpp:188]
[2025.06.13-13.15.51:528][736]LogWindows: Error: [Callstack] 0x00007fffccbd1a23 UnrealEditor-Core.dll!FThreadImpl::Run() [D:\build\++UE5\Sync\Engine\Source\Runtime\Core\Private\HAL\Thread.cpp:69]
[2025.06.13-13.15.51:528][736]LogWindows: Error: [Callstack] 0x00007fffcd0737ad UnrealEditor-Core.dll!FRunnableThreadWin::Run() [D:\build\++UE5\Sync\Engine\Source\Runtime\Core\Private\Windows\WindowsRunnableThread.cpp:159]
[2025.06.13-13.15.51:528][736]LogWindows: Error: [Callstack] 0x00007fffcd06c8ff UnrealEditor-Core.dll!FRunnableThreadWin::GuardedRun() [D:\build\++UE5\Sync\Engine\Source\Runtime\Core\Private\Windows\WindowsRunnableThread.cpp:79]
[2025.06.13-13.15.51:528][736]LogWindows: Error: [Callstack] 0x00007ff86d31e8d7 KERNEL32.DLL!UnknownFunction []
[2025.06.13-13.15.51:528][736]LogWindows: Error:
[2025.06.13-13.15.51:528][736]LogWindows: Error: Crash in runnable thread Foreground Worker #1
[2025.06.13-13.15.56:535][736]LogExit: Executing StaticShutdownAfterError