This will occur when changing between all Import Types (so long as Create Materials is checked). The callstacks are slightly different depending on which Import Type you switch to.
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REPRO STEPS:
RESULT:
Editor crashes
Access violation - code c0000005 (first/second chance not available) UE4Editor_Engine!UMaterialInterface::GetRelevance_Concurrent() materialinterface.cpp:116 UE4Editor_Engine!UMeshComponent::GetMaterialRelevance() meshcomponent.cpp:87 UE4Editor_GeometryCache!FGeometryCacheSceneProxy::FGeometryCacheSceneProxy() geometrycachesceneproxy.cpp:10 UE4Editor_GeometryCache!UGeometryCacheComponent::CreateSceneProxy() geometrycachecomponent.cpp:155 UE4Editor_Renderer!FScene::AddPrimitive() rendererscene.cpp:633 UE4Editor_Engine!UActorComponent::RecreateRenderState_Concurrent() actorcomponent.cpp:1202 UE4Editor_GeometryCacheEd!FGeometryCacheThumbnailScene::SetGeometryCache() geometrycachethumbnailscene.cpp:39 UE4Editor_GeometryCacheEd!UGeometryCacheThumbnailRenderer::Draw() geometrycachethumbnailrenderer.cpp:29 UE4Editor_UnrealEd!ThumbnailTools::RenderThumbnail() objecttools.cpp:3816 UE4Editor_UnrealEd!FAssetThumbnailPool::Tick() assetthumbnail.cpp:969 UE4Editor_UnrealEd!FTickableEditorObject::TickObjects() tickableeditorobject.h:17 UE4Editor_UnrealEd!UEditorEngine::Tick() editorengine.cpp:1181 UE4Editor_UnrealEd!UUnrealEdEngine::Tick() unrealedengine.cpp:371 UE4Editor!FEngineLoop::Tick() launchengineloop.cpp:2834 UE4Editor!GuardedMain() launch.cpp:156 UE4Editor!GuardedMainWrapper() launchwindows.cpp:126 UE4Editor!WinMain() launchwindows.cpp:202 UE4Editor!__scrt_common_main_seh() exe_common.inl:264 kernel32!<Unknown> ntdll!<Unknown>
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-34377 in the post.