I have the same problem with Unreal Engine 4.26
I have created a new project from the 3d first person shooter C++ template, created a custom GameInstance class with no logic yet (so no custom made code involved in the game at this point).
And my Unreal Editor also crashed at random times (usually though when exiting PIE)
Crash Log:
Fatal error: [File:D:/Build/++UE4/Sync/Engine/Source/Runtime/Core/Private/Windows/WindowsPlatformMisc.cpp] [Line: 475] Pure virtual function being called
UE4Editor_Core!PureCallHandler() [D:\Build\++UE4\Sync\Engine\Source\Runtime\Core\Private\Windows\WindowsPlatformMisc.cpp:477]
VCRUNTIME140
UE4Editor_CoreUObject!UGCObjectReferencer::AddReferencedObjects() [D:\Build\++UE4\Sync\Engine\Source\Runtime\CoreUObject\Private\Misc\GCObjectReferencer.cpp:27]
UE4Editor_CoreUObject!TFastReferenceCollector<FGCReferenceProcessor<1>,FGCCollector<1>,FGCArrayPool,1>::ProcessObjectArray() [D:\Build\++UE4\Sync\Engine\Source\Runtime\CoreUObject\Public\UObject\FastReferenceCollector.h:881]
UE4Editor_CoreUObject!TFastReferenceCollector<FGCReferenceProcessor<1>,FGCCollector<1>,FGCArrayPool,1>::FCollectorTaskQueue::DoTask() [D:\Build\++UE4\Sync\Engine\Source\Runtime\CoreUObject\Public\UObject\FastReferenceCollector.h:403]
UE4Editor_CoreUObject!TGraphTask<TFastReferenceCollector<FGCReferenceProcessor<1>,FGCCollector<1>,FGCArrayPool,1>::FCollectorTaskProcessorTask>::ExecuteTask() [D:\Build\++UE4\Sync\Engine\Source\Runtime\Core\Public\Async\TaskGraphInterfaces.h:886]
UE4Editor_Core!FTaskThreadAnyThread::ProcessTasks() [D:\Build\++UE4\Sync\Engine\Source\Runtime\Core\Private\Async\TaskGraph.cpp:1065]
UE4Editor_Core!FTaskThreadAnyThread::ProcessTasksUntilQuit() [D:\Build\++UE4\Sync\Engine\Source\Runtime\Core\Private\Async\TaskGraph.cpp:888]
UE4Editor_Core!FTaskThreadAnyThread::Run() [D:\Build\++UE4\Sync\Engine\Source\Runtime\Core\Private\Async\TaskGraph.cpp:965]
UE4Editor_Core!FRunnableThreadWin::Run() [D:\Build\++UE4\Sync\Engine\Source\Runtime\Core\Private\Windows\WindowsRunnableThread.cpp:86]