I am getting this error only when including a level in the packaged build.
I also tried converting the level to world partition, same error.
I am using Engine version 5.4.4.
PackagingResults: Error: Assertion failed: InWorld != ReferencedWorld [File:D:\build++UE5\Sync\Engine\Source\Runtime\Engine\Private\WorldPartition\WorldPartitionCookPackageSplitter.cpp] [Line: 58] PackagingResults: Error: [Cook] World /Game/Medieval_Bundle/CastleTown/Levels/SubLevels/SL_Landscape.SL_Landscape is being cleaned up while still referenced by a package splitter.