Cannot play standalone/offline in editor since upgrading to 4.26

I upgraded my game which runs on a dedicated server from 4.25.3 to 4.26 (source built) and cannot run the game offline anymore, it just crashes. Running the game in listen-server or dedicated server mode works fine. Running an empty map with no gamemode and only the default pawn etc. also crashes.

I’ve checked my blueprints for any dedicated server and Has Authority? checks but I can’t seem to find the problem. Has anyone else had problems upgrading to 4.26 with a dedicated server? Data validation of all my assets also yielded no results and produced no errors.

Here is the log produced by the crash:


Assertion failed: !GIsPlayInEditorWorld [File D:/Unreal/UE426/Engine/Source/Editor/UnrealEd/Private/Editor.cpp] [Line: 817]

UE4Editor_Core!AssertFailedImplV() [d:\unreal\ue426\engine\source\runtime\core\private\misc\assertionmacros.cpp:102]
UE4Editor_Core!FDebug::CheckVerifyFailedImpl() [d:\unreal\ue426\engine\source\runtime\core\private\misc\assertionmacros.cpp:458]
UE4Editor_UnrealEd!SetPlayInEditorWorld() [d:\unreal\ue426\engine\source\editor\unrealed\private\editor.cpp:817]
UE4Editor_UnrealEd!UEditorEngine::CreateInnerProcessPIEGameInstance() [d:\unreal\ue426\engine\source\editor\unrealed\private\playlevel.cpp:2795]
UE4Editor_UnrealEd!UEditorEngine::OnLoginPIEComplete_Deferred() [d:\unreal\ue426\engine\source\editor\unrealed\private\playlevel.cpp:1503]
UE4Editor_UnrealEd!UEditorEngine::CreateNewPlayInEditorInstance() [d:\unreal\ue426\engine\source\editor\unrealed\private\playlevel.cpp:1750]
UE4Editor_UnrealEd!UEditorEngine::StartPlayInEditorSession() [d:\unreal\ue426\engine\source\editor\unrealed\private\playlevel.cpp:2700]
UE4Editor_UnrealEd!UEditorEngine::StartQueuedPlaySessionRequestImpl() [d:\unreal\ue426\engine\source\editor\unrealed\private\playlevel.cpp:1116]
UE4Editor_UnrealEd!UEditorEngine::StartQueuedPlaySessionRequest() [d:\unreal\ue426\engine\source\editor\unrealed\private\playlevel.cpp:1019]
UE4Editor_UnrealEd!UEditorEngine::Tick() [d:\unreal\ue426\engine\source\editor\unrealed\private\editorengine.cpp:1622]
UE4Editor_UnrealEd!UUnrealEdEngine::Tick() [d:\unreal\ue426\engine\source\editor\unrealed\private\unrealedengine.cpp:426]
UE4Editor!FEngineLoop::Tick() [d:\unreal\ue426\engine\source\runtime\launch\private\launchengineloop.cpp:4834]
UE4Editor!GuardedMain() [d:\unreal\ue426\engine\source\runtime\launch\private\launch.cpp:169]
UE4Editor!GuardedMainWrapper() [d:\unreal\ue426\engine\source\runtime\launch\private\windows\launchwindows.cpp:137]
UE4Editor!WinMain() [d:\unreal\ue426\engine\source\runtime\launch\private\windows\launchwindows.cpp:268]
UE4Editor!__scrt_common_main_seh() [d:\agent\_work\2\s\src\vctools\crt\vcstartup\src\startup\exe_common.inl:288]

Update: I no longer experience this problem after updating my 4.25.3 project to 4.26.1. Everything seems to work smoothly now.

I do have the same problem. it works if I load a level with client-only, but will always fail with the same error if I try in offline mode. It was working fine before 4.26

Have this problem in a new C++ 4.26 project. Another test project migrated from 4.25 to 4.26 works fine. At the same time after build when trying to either create or join session - the game restarts and the connection does not happen. Anyone?

Update: I no longer experience this problem after updating my 4.25.3 project to 4.26.1. Everything seems to work smoothly now.