This is a somewhat common crash that has existed since at least 4.14.. It appears related to an Undo operation on geometry.
User Descriptions
Source Context
150 void UModelComponent::CommitSurfaces()
151 {
152 TArray<int32> InvalidElements;
153
154 // Find nodes that are from surfaces which have been invalidated.
155 TMap<uint16,FModelElement*> InvalidNodes;
156 for(int32 ElementIndex = 0;ElementIndex < Elements.Num();ElementIndex++)
157 {
158 FModelElement& Element = Elements[ElementIndex];
159 TArray<uint16> NewNodes;
160 for(int32 NodeIndex = 0;NodeIndex < Element.Nodes.Num();NodeIndex++)
161 {
162 ***** FBspNode& Node = Model->Nodes[Element.Nodes[NodeIndex]];
163 FBspSurf& Surf = Model->Surfs[Node.iSurf];
164 if(Surf.Material != Element.Material)
165 {
166 // This node's material changed, remove it from the element and put it on the invalid node list.
167 InvalidNodes.Add(Element.Nodes[NodeIndex],&Element);
168
169 // Mark the node's original element as being invalid.
170 InvalidElements.AddUnique(ElementIndex);
171 }
172 else
173 {
174 NewNodes.Add(Element.Nodes[NodeIndex]);
175 }
176 }
repro steps currently unknown, but seems to occur during a geometry Undo
Assertion failed: (Index >= 0) & (Index < ArrayNum) [File:D:\Build\++UE4+Release-4.18+Compile\Sync\Engine\Source\Runtime\Core\Public\Containers/Array.h] [Line: 610] Array index out of bounds: 836 from an array of size 816 UE4Editor_Engine!UModelComponent::CommitSurfaces() [modelcomponent.cpp:163] UE4Editor_Engine!ULevel::CommitModelSurfaces() [level.cpp:1493] UE4Editor_Engine!UWorld::CommitModelSurfaces() [world.cpp:1817] UE4Editor_UnrealEd!UEditorEngine::Tick() [editorengine.cpp:1777] UE4Editor_UnrealEd!UUnrealEdEngine::Tick() [unrealedengine.cpp:396] UE4Editor!FEngineLoop::Tick() [launchengineloop.cpp:3296] UE4Editor!GuardedMain() [launch.cpp:166] UE4Editor!GuardedMainWrapper() [launchwindows.cpp:134] UE4Editor!WinMain() [launchwindows.cpp:210] UE4Editor!__scrt_common_main_seh() [exe_common.inl:253] kernel32!BaseThreadInitThunk() ntdll!RtlUserThreadStart()
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-51632 in the post.