Crash when attempting to merge two objects using Simplygon - ProxyMaterialUtilities::CreateProxyMaterialInstance

Engine crashes on completing a simplygon merge of two actors

Note If you set On screen size to 50, you can speed up the merge to get to the crash quicker

1. Compile and open the editor
2. Open QAGame
3. Locate asset Test_LavaKnight in the content browser
4. Click floor in the level
5. In the static mesh editor click on Window, Developer tools, Merge Actors.
6. In the merge actors window click the 2nd Tab
   Harvest geometry from selected actors and merge them into single mesh
7. Click Merge actors
8. Select the Content folder as the save location name the save Test
   Result
   As you finish generating the mesh the editor will crash

UE4Editor_MeshUtilities!ProxyMaterialUtilities::CreateProxyMaterialInstance() proxymaterialutilities.h:92
UE4Editor_MeshUtilities!FProxyGenerationProcessor::ProcessJob() meshutilities.cpp:376
UE4Editor_MeshUtilities!FProxyGenerationProcessor::Tick() meshutilities.cpp:289
UE4Editor_MeshUtilities!FMeshUtilities::CreateProxyMesh() meshutilities.cpp:5540
UE4Editor_MergeActors!FMeshProxyTool::RunMerge() meshproxytool.cpp:120
UE4Editor_MergeActors!SMergeActorsToolbar::OnMergeActorsClicked() smergeactorstoolbar.cpp:132
UE4Editor_MergeActors!TMemberFunctionCaller<SMergeActorsToolbar,FReply() delegateinstanceinterface.h:161
UE4Editor_MergeActors!TTupleImpl<TIntegerSequence<unsigned int> >::ApplyAfter<TMemberFunctionCaller<SMergeActorsToolbar,FReply() tuple.h:115
UE4Editor_MergeActors!TBaseSPMethodDelegateInstance<0,SMergeActorsToolbar,0,FReply __cdecl() delegateinstancesimpl.h:317
UE4Editor_Slate!TBaseDelegate<FReply>::Execute() delegatesignatureimpl.inl:521
UE4Editor_Slate!SButton::OnMouseButtonUp() sbutton.cpp:278
UE4Editor_Slate!<lambda_8d0e9a1da76abd0a756a3a9d775f5ed1>::operator() slateapplication.cpp:4901
UE4Editor_Slate!FEventRouter::Route<FReply,FEventRouter::FToLeafmostPolicy,FPointerEvent,<lambda_8d0e9a1da76abd0a756a3a9d775f5ed1> >() slateapplication.cpp:215
UE4Editor_Slate!FSlateApplication::RoutePointerUpEvent() slateapplication.cpp:4890
UE4Editor_Slate!FSlateApplication::ProcessMouseButtonUpEvent() slateapplication.cpp:5348
UE4Editor_Slate!FSlateApplication::OnMouseUp() slateapplication.cpp:5328
UE4Editor_Core!FWindowsApplication::ProcessDeferredMessage() windowsapplication.cpp:1584
UE4Editor_Core!FWindowsApplication::DeferMessage() windowsapplication.cpp:1930
UE4Editor_Core!FWindowsApplication::ProcessMessage() windowsapplication.cpp:747
UE4Editor_Core!FWindowsApplication::AppWndProc() windowsapplication.cpp:669
user32!<Unknown>
user32!<Unknown>
UE4Editor_Core!FWindowsPlatformMisc::PumpMessages() windowsplatformmisc.cpp:905
UE4Editor!FEngineLoop::Tick() launchengineloop.cpp:2788
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>