Crash when generating proxy mesh

Generating a proxy mesh with imported models and the simplify mesh flag set to true causes the editor to crash.

Tested in 4.21.2 (CL - 4753647), 4.22.3 (CL - 7053647), 4.23 (CL - 7288428), 4.24 (CL - 7285696)

1. Download the attached project
2. Open the Hierarchial LOD Outliner
3. Generate Clusters
4. Under Hierarchial LODSetup, select Simplify Mesh
5. Generate Proxy Meshes or Rebuild All

Expected: The a simplified proxy mesh would be generated

Result: The editor crashes

LoginId:5964f8f84766f4b976277180442869c1
EpicAccountId:d237bdd466454ba6a10848877d154538

Assertion failed: Remap.IsValidIndex(PolygonGroupID.GetValue()) [Link Removed] [Line: 1465] Missing material bake output index entry for mesh(section)

UE4Editor_Core!FWindowsErrorOutputDevice::Serialize() [e:\daniel.hamilton_ue4main\engine\source\runtime\core\private\windows\windowserroroutputdevice.cpp:79]
UE4Editor_Core!FOutputDevice::LogfImpl() [e:\daniel.hamilton_ue4main\engine\source\runtime\core\private\misc\outputdevice.cpp:71]
UE4Editor_Core!AssertFailedImplV() [e:\daniel.hamilton_ue4main\engine\source\runtime\core\private\misc\assertionmacros.cpp:101]
UE4Editor_Core!FDebug::CheckVerifyFailedImpl() [e:\daniel.hamilton_ue4main\engine\source\runtime\core\private\misc\assertionmacros.cpp:445]
UE4Editor_MeshMergeUtilities!<lambda_11f116a974b3ed6470c2828b3ddce8bc>::operator()() [e:\daniel.hamilton_ue4main\engine\source\developer\meshmergeutilities\private\meshmergeutilities.cpp:1465]
UE4Editor_ProxyLODMeshReduction!<lambda_de641a5da653da9c71c6c3a24fcacab6>::operator()() [e:\daniel.hamilton_ue4main\engine\plugins\experimental\proxylodplugin\source\proxylod\private\proxylodplugin.cpp:875]
UE4Editor_ProxyLODMeshReduction!tbb::internal::task_group_base::internal_run_and_wait<<lambda_de641a5da653da9c71c6c3a24fcacab6> const >() [e:\daniel.hamilton_ue4main\engine\source\thirdparty\inteltbb\inteltbb-4.4u3\include\tbb\task_group.h:91]
UE4Editor_ProxyLODMeshReduction!FVoxelizeMeshMerging::ProxyLOD() [e:\daniel.hamilton_ue4main\engine\plugins\experimental\proxylodplugin\source\proxylod\private\proxylodplugin.cpp:869]
UE4Editor_MeshMergeUtilities!FMeshMergeUtilities::CreateProxyMesh() [e:\daniel.hamilton_ue4main\engine\source\developer\meshmergeutilities\private\meshmergeutilities.cpp:1574]
UE4Editor_HierarchicalLODUtilities!FHierarchicalLODUtilities::BuildStaticMeshForLODActor() [e:\daniel.hamilton_ue4main\engine\source\developer\hierarchicallodutilities\private\hierarchicallodutilities.cpp:418]
UE4Editor_HierarchicalLODUtilities!FHierarchicalLODUtilities::BuildStaticMeshForLODActor() [e:\daniel.hamilton_ue4main\engine\source\developer\hierarchicallodutilities\private\hierarchicallodutilities.cpp:233]
UE4Editor_UnrealEd!FHierarchicalLODBuilder::BuildMeshesForLODActors() [e:\daniel.hamilton_ue4main\engine\source\editor\unrealed\private\hierarchicallod.cpp:726]
UE4Editor_HierarchicalLODOutliner!<lambda_54dc5f3e535b305158d197f37ea80386>::operator()() [e:\daniel.hamilton_ue4main\engine\source\editor\hierarchicallodoutliner\private\hlodoutliner.cpp:798]
UE4Editor_HierarchicalLODOutliner!HLODOutliner::SHLODOutliner::HandleBuildLODActors() [e:\daniel.hamilton_ue4main\engine\source\editor\hierarchicallodoutliner\private\hlodoutliner.cpp:819]
UE4Editor_HierarchicalLODOutliner!TBaseSPMethodDelegateInstance<0,HLODOutliner::SHLODOutliner,0,FReply __cdecl(void)>::Execute() [e:\daniel.hamilton_ue4main\engine\source\runtime\core\public\delegates\delegateinstancesimpl.h:293]
UE4Editor_Slate!SButton::ExecuteOnClick() [e:\daniel.hamilton_ue4main\engine\source\runtime\slate\private\widgets\input\sbutton.cpp:379]
UE4Editor_Slate!SButton::OnMouseButtonUp() [e:\daniel.hamilton_ue4main\engine\source\runtime\slate\private\widgets\input\sbutton.cpp:303]
UE4Editor_Slate!FEventRouter::Route<FReply,FEventRouter::FToLeafmostPolicy,FPointerEvent,<lambda_6c1f6b862bcfb82ea6dcab28fbcc9463> >() [e:\daniel.hamilton_ue4main\engine\source\runtime\slate\private\framework\application\slateapplication.cpp:273]
UE4Editor_Slate!FSlateApplication::RoutePointerUpEvent() [e:\daniel.hamilton_ue4main\engine\source\runtime\slate\private\framework\application\slateapplication.cpp:5631]
UE4Editor_Slate!FSlateApplication::ProcessMouseButtonUpEvent() [e:\daniel.hamilton_ue4main\engine\source\runtime\slate\private\framework\application\slateapplication.cpp:6236]
UE4Editor_Slate!FSlateApplication::OnMouseUp() [e:\daniel.hamilton_ue4main\engine\source\runtime\slate\private\framework\application\slateapplication.cpp:6209]
UE4Editor_ApplicationCore!FWindowsApplication::ProcessDeferredMessage() [e:\daniel.hamilton_ue4main\engine\source\runtime\applicationcore\private\windows\windowsapplication.cpp:1880]
UE4Editor_ApplicationCore!FWindowsApplication::DeferMessage() [e:\daniel.hamilton_ue4main\engine\source\runtime\applicationcore\private\windows\windowsapplication.cpp:2332]
UE4Editor_ApplicationCore!FWindowsApplication::ProcessMessage() [e:\daniel.hamilton_ue4main\engine\source\runtime\applicationcore\private\windows\windowsapplication.cpp:1560]
UE4Editor_ApplicationCore!FWindowsApplication::AppWndProc() [e:\daniel.hamilton_ue4main\engine\source\runtime\applicationcore\private\windows\windowsapplication.cpp:790]
user32
user32
UE4Editor_ApplicationCore!FWindowsPlatformApplicationMisc::PumpMessages() [e:\daniel.hamilton_ue4main\engine\source\runtime\applicationcore\private\windows\windowsplatformapplicationmisc.cpp:123]
UE4Editor!FEngineLoop::Tick() [e:\daniel.hamilton_ue4main\engine\source\runtime\launch\private\launchengineloop.cpp:4168]
UE4Editor!GuardedMain() [e:\daniel.hamilton_ue4main\engine\source\runtime\launch\private\launch.cpp:173]
UE4Editor!GuardedMainWrapper() [e:\daniel.hamilton_ue4main\engine\source\runtime\launch\private\windows\launchwindows.cpp:147]
UE4Editor!WinMain() [e:\daniel.hamilton_ue4main\engine\source\runtime\launch\private\windows\launchwindows.cpp:279]
UE4Editor!__scrt_common_main_seh() [d:\agent\_work\1\s\src\vctools\crt\vcstartup\src\startup\exe_common.inl:288]
kernel32
ntdll