[4.18.2] editor crash while testing multiplayer

Development Programming & Scripting Multiplayer & Networking
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1

editor crash trying to join a multiplayer game in PIE with single process (auto-join disabled in editor settings)

Assertion failed: Property->PropertyFlags & CPF_Net [File:D:\Build++UE4+Release-4.18+Compile\Sync\Engine\Source\Runtime\Engine\Private\RepLayout.cpp] [Line: 2975]

0x0000000034EC3FB8 KERNELBASE.dll!UnknownFunction []
0x00000000096576D4 UE4Editor-ApplicationCore.dll!FWindowsErrorOutputDevice::Serialize() [d:\build\++ue4+release-4.18+compile\sync\engine\source\runtime\applicationcore\private\windows\windowserroroutputdevice.cpp:65]
0x00000000FAC6330B UE4Editor-Core.dll!FOutputDevice::Logf__VA() [d:\build\++ue4+release-4.18+compile\sync\engine\source\runtime\core\private\misc\outputdevice.cpp:70]
0x00000000FABF47F9 UE4Editor-Core.dll!FDebug::AssertFailed() [d:\build\++ue4+release-4.18+compile\sync\engine\source\runtime\core\private\misc\assertionmacros.cpp:414]
0x00000000F8EE0A4E UE4Editor-Engine.dll!FRepLayout::InitFromObjectClass() [d:\build\++ue4+release-4.18+compile\sync\engine\source\runtime\engine\private\replayout.cpp:2977]
0x00000000F8C29349 UE4Editor-Engine.dll!UNetDriver::GetObjectClassRepLayout() [d:\build\++ue4+release-4.18+compile\sync\engine\source\runtime\engine\private\networkdriver.cpp:3612]
0x00000000F8C227A5 UE4Editor-Engine.dll!UNetDriver::FindOrCreateRepChangedPropertyTracker() [d:\build\++ue4+release-4.18+compile\sync\engine\source\runtime\engine\private\networkdriver.cpp:3596]
0x00000000F8140CFD UE4Editor-Engine.dll!AActor::CallPreReplication() [d:\build\++ue4+release-4.18+compile\sync\engine\source\runtime\engine\private\actor.cpp:956]
0x00000000F8C53CFC UE4Editor-Engine.dll!UNetDriver::ServerReplicateActors_BuildConsiderList() [d:\build\++ue4+release-4.18+compile\sync\engine\source\runtime\engine\private\networkdriver.cpp:2718]
0x00000000F8C519E6 UE4Editor-Engine.dll!UNetDriver::ServerReplicateActors() [d:\build\++ue4+release-4.18+compile\sync\engine\source\runtime\engine\private\networkdriver.cpp:3185]
0x00000000F8C5B4F5 UE4Editor-Engine.dll!UNetDriver::TickFlush() [d:\build\++ue4+release-4.18+compile\sync\engine\source\runtime\engine\private\networkdriver.cpp:369]
0x00000000F8C2065F UE4Editor-Engine.dll!TBaseUObjectMethodDelegateInstance<0,UNetDriver,void __cdecl(float)>::ExecuteIfSafe() [d:\build\++ue4+release-4.18+compile\sync\engine\source\runtime\core\public\delegates\delegateinstancesimpl.h:858]
0x00000000F807CF78 UE4Editor-Engine.dll!TBaseMulticastDelegate<void,float>::Broadcast() [d:\build\++ue4+release-4.18+compile\sync\engine\source\runtime\core\public\delegates\delegatesignatureimpl.inl:937]
0x00000000F8AC858D UE4Editor-Engine.dll!UWorld::Tick() [d:\build\++ue4+release-4.18+compile\sync\engine\source\runtime\engine\private\leveltick.cpp:1553]
0x00000000F6CA6BA6 UE4Editor-UnrealEd.dll!UEditorEngine::Tick() [d:\build\++ue4+release-4.18+compile\sync\engine\source\editor\unrealed\private\editorengine.cpp:1659]
0x00000000F7554AC6 UE4Editor-UnrealEd.dll!UUnrealEdEngine::Tick() [d:\build\++ue4+release-4.18+compile\sync\engine\source\editor\unrealed\private\unrealedengine.cpp:396]
0x000000005AA15A26 UE4Editor.exe!FEngineLoop::Tick() [d:\build\++ue4+release-4.18+compile\sync\engine\source\runtime\launch\private\launchengineloop.cpp:3296]
0x000000005AA25430 UE4Editor.exe!GuardedMain() [d:\build\++ue4+release-4.18+compile\sync\engine\source\runtime\launch\private\launch.cpp:166]
0x000000005AA254AA UE4Editor.exe!GuardedMainWrapper() [d:\build\++ue4+release-4.18+compile\sync\engine\source\runtime\launch\private\windows\launchwindows.cpp:134]
0x000000005AA32379 UE4Editor.exe!WinMain() [d:\build\++ue4+release-4.18+compile\sync\engine\source\runtime\launch\private\windows\launchwindows.cpp:210]
0x000000005AA33D57 UE4Editor.exe!__scrt_common_main_seh() [f:\dd\vctools\crt\vcstartup\src\startup\exe_common.inl:253]
0x00000000355F1FE4 KERNEL32.DLL!UnknownFunction []
0x0000000037DDEF91 ntdll.dll!UnknownFunction []
0x0000000037DDEF91 ntdll.dll!UnknownFunction []
2

RepLayout.cpp [2970]:

	for ( int32 i = 0; i < InObjectClass->ClassReps.Num(); i++ )
	{
		UProperty * Property	= InObjectClass->ClassReps[i].Property;
		const int32 ArrayIdx	= InObjectClass->ClassReps[i].Index;

		check( Property->PropertyFlags & CPF_Net ); // <------ engine crash here

ClassReps array contains 32 elements, but they are nulls from index 21.
Deleting saved and intermediate folders, refreshing nodes on crashing classes, DID NOT solve the issue.

3

if I edit a single blueprint (set to none a replicated var and set it back to replicated), recompile it and then start game in pie, blueprint doesn’t crash.
if I close unreal and start it again issue is still there.

We can’t recompile each replicated bp whenever we start ue editor :frowning:

This is 3rd blocking bug we faced in last month (child bp crashing upgrading from 4.17 + vr mode slate crash)… this is totally disappointing

4

it seems to be a well known bug…

https://answers.unrealengine.com/questions/516676/editorcrashwhenmultipie.html
https://answers.unrealengine.com/questions/393022/assertion-failed-parentsiproperty-repindex-parents.html
https://answers.unrealengine.com/questions/397989/blueprint-replication-problems-on-transition-to-41.html
https://answers.unrealengine.com/questions/607913/assertion-failed-property-propertyflags-cpf-net-1.html?sort=oldest

5

I noticed problem occurs when repnotified var is declared on a child blueprint

6

Ok managed to solve it… we ported all replicated vars in native c++ classes.
Now we can freely test multiplayer in PIE.

It was a huge work, but now we have a foundation to port progressively all our project.

Someone should advice new users that blueprints are highly unstable.
They’re definitely NOT suited to develop a non trivial project.

7

Epic this shouldn’t be marked as solved…