User comments in crash group:
1628 if (HasTessellationEnabled)
1629 {
1630 ***** UMaterialInstance* NonTessellatedLandscapeMI = Cast<UMaterialInstance>(AvailableMaterials[MaterialIndexToDisabledTessellationMaterial[i]]);
1631
1632 // Make sure that the Material instance we are going to use has the tessellation disabled
1633 UMaterialInstanceDynamic* NonTessellatedLandscapeMID = Cast<UMaterialInstanceDynamic>(NonTessellatedLandscapeMI);
1634 ULandscapeMaterialInstanceConstant* NonTessellatedLandscapeMIC = Cast<ULandscapeMaterialInstanceConstant>(NonTessellatedLandscapeMI);
1635
1636 if (NonTessellatedLandscapeMID != nullptr)
1637 {
1638 NonTessellatedLandscapeMIC = Cast<ULandscapeMaterialInstanceConstant>(NonTessellatedLandscapeMID->Parent);
1639 }
The issue was happening when creating a new landscape with a material (but not having a layer info object assigned to any layer, then simply enable flat tessellation in the landscape material.
It would crash as it was assumed we needed something painted on the landscape to apply tessellation.
Assertion failed: (Index >= 0) & (Index < ArrayNum) [File:D:\Build\++UE4\Sync\Engine\Source\Runtime\Core\Public\Containers/Array.h] [Line: 611] Array index out of bounds: -1 from an array of size 1 UE4Editor_Landscape!FLandscapeComponentSceneProxy::DrawStaticElements() [landscaperender.cpp:1631] UE4Editor_Renderer!FPrimitiveSceneInfo::AddStaticMeshes() [primitivesceneinfo.cpp:152] UE4Editor_Renderer!FPrimitiveSceneInfo::AddToScene() [primitivesceneinfo.cpp:211] UE4Editor_Renderer!FScene::AddPrimitiveSceneInfo_RenderThread() [rendererscene.cpp:653] UE4Editor_Renderer!<lambda_62fe13b83733dfa58d31fcd06f4bbe45>::operator() [rendererscene.cpp:880] UE4Editor_Renderer!TGraphTask<TEnqueueUniqueRenderCommandType<`FScene::AddPrimitive'::`2'::AddPrimitiveCommandName,<lambda_62fe13b83733dfa58d31fcd06f4bbe45> > >::ExecuteTask() [taskgraphinterfaces.h:829] UE4Editor_Core!FNamedTaskThread::ProcessTasksNamedThread() [taskgraph.cpp:679] UE4Editor_Core!FNamedTaskThread::ProcessTasksUntilQuit() [taskgraph.cpp:575] UE4Editor_RenderCore!RenderingThreadMain() [renderingthread.cpp:333] UE4Editor_RenderCore!FRenderingThread::Run() [renderingthread.cpp:467] UE4Editor_Core!FRunnableThreadWin::Run() [windowsrunnablethread.cpp:76]
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-66155 in the post.