This is a common assertion that has occurred since at least 4.14 and affected nearly 100 users.
The callstack is similar to [Link Removed], which was marked fixed for 4.14.
User Descriptions
Source Context
1599 AWorldSettings* ULevel::GetWorldSettings(bool bChecked) const 1600 { 1601 if (bChecked) 1602 { 1603 ***** checkf( WorldSettings != nullptr, *GetPathName() ); 1604 } 1605 return WorldSettings; 1606 } 1607 1608 void ULevel::SetWorldSettings(AWorldSettings* NewWorldSettings) 1609 {
repro steps currently unknown
Assertion failed: WorldSettings != nullptr [File:D:\Build\++UE4+Release-4.17+Compile\Sync\Engine\Source\Runtime\Engine\Private\Level.cpp] [Line: 1604] /Engine/Transient.World_1:PersistentLevel UE4Editor_Engine!ULevel::GetWorldSettings() [level.cpp:1604] UE4Editor_Engine!UWorld::GetWorldSettings() [world.cpp:3855] UE4Editor_Engine!UWorld::IsPaused() [leveltick.cpp:437] UE4Editor_Engine!UWorld::IsCameraMoveable() [leveltick.cpp:446] UE4Editor_Engine!FSceneViewFamily::FSceneViewFamily() [sceneview.cpp:2362] UE4Editor_UnrealEd!UMaterialInstanceThumbnailRenderer::Draw() [materialinstancethumbnailrenderer.cpp:31] UE4Editor_UnrealEd!ThumbnailTools::RenderThumbnail() [objecttools.cpp:3657] UE4Editor_UnrealEd!FAssetThumbnailPool::Tick() [assetthumbnail.cpp:1002] UE4Editor_UnrealEd!FTickableEditorObject::TickObjects() [tickableeditorobject.h:21] UE4Editor_UnrealEd!UEditorEngine::Tick() [editorengine.cpp:1424] UE4Editor_UnrealEd!UUnrealEdEngine::Tick() [unrealedengine.cpp:402] UE4Editor!FEngineLoop::Tick() [launchengineloop.cpp:3215] 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-48997 in the post.