UnrealLightmass stops unexpectedly


I have a map in which I’m trying to build lighting, however UnrealLightmass stops unexpectedly without any reason (and with any quality). This is the first time it ever happen in my case.

SwarmAgent log:

21:38:44: LogWindows: Warning: CreateProc failed (2) …/…/…/Engine/Binaries/Win64/CrashReportClient.exe “D:/…/AppData/Local/UnrealEngine/4.17/Saved/Swarm/Engine/Programs/UnrealLightmass/Saved/Crashes/_0000” -AppName=UE4-UnrealLightmass -CrashGUID=_0000 -DebugSymbols=…....\Engine\Intermediate\Symbols

21:38:44: [Job] Job has failed! Job executable didn’t exit cleanly. Exit code: 1

According to the generated minidump :

Exception Code : 0xC0000005

Exception Information: The thread tried to read from or write to a virtual address for which it does not have the appropriate access.

To avoid issues with privacy I would like to send my crash dump privately to an UE support guy or developer in case it would help.


I debugged a lightmass crash in 4.16 last night which could cause the logs you have entered. In our case the data in the Swarm Cache was stale caused the LOD data to be very incorrect. Cleaning out the SwarmCache folder fixes the issue as a work around. I’m not sure how we managed to get our cached data into that state but this could alleviate the crashes you experience