This is a common and longstanding crash that has occurred since at least 4.15.
Originally this was being tracked under [Link Removed] due to sharing the same callstack, but that had specific repro steps that have been confirmed fixed for 4.18, while users are still hitting this callstack in 4.18.
Source Context
10650 if (WorldContext.World()->GetNetMode() == NM_Client) 10651 { 10652 WorldContext.LastRemoteURL = URL; 10653 } 10654 10655 // Spawn play actors for all active local players 10656 if (WorldContext.OwningGameInstance != NULL) 10657 { 10658 for(auto It = WorldContext.OwningGameInstance->GetLocalPlayerIterator(); It; ++It) 10659 { 10660 FString Error2; 10661 if(!(*It)->SpawnPlayActor(URL.ToString(1),Error2,WorldContext.World())) 10662 { 10663 ***** UE_LOG(LogEngine, Fatal, TEXT("Couldn't spawn player: %s"), *Error2); 10664 } 10665 } 10666 }
repro steps currently unknown
Assertion failed: NewWorld [File:D:\Build\++UE4+Release-4.18+Compile\Sync\Engine\Source\Runtime\Engine\Private\UnrealEngine.cpp] [Line: 10494] UE4Editor_Engine!UEngine::LoadMap() unrealengine.cpp:10496 UE4Editor_Engine!UEngine::Browse() unrealengine.cpp:9948 UE4Editor_Engine!UEngine::TickWorldTravel() unrealengine.cpp:10137 UE4Editor_UnrealEd!UEditorEngine::Tick() editorengine.cpp:1605 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-51948 in the post.