World composition async level loading is blocking

I am using world composition (4.18.2) and when a level is being loaded, this is blocking the entire UI, even though some of the processing is supposed to be made asynchronously (LoadPackageAsync is being called, Project Settings has Async Loading Thread enabled).
Also, when a level is unloaded due to view distance, the UI completely freezes and never recovers unless I quit the game (ESC key in Editor).
Is async loading in world composition supported? If so how do we make it work?

Update: after debugging it seems FAsyncLoadingThread is never started, so all supposedly async loading is being made in the main thread. How come?

found out that async loading is working only when game is cooked… very annoying, can UE devs please look into this? (check function FAsyncLoadingThread::ShouldBeMultithreaded())

I still have the problem of game locking up on level unload though…

For those interested, I found out about the problem of game locking up on level unload: this was a mistake on my side, I instantiated the player pawn into a streaming level instead of the persistent level, so when the streaming level was unloaded, the player pawn was destroyed! To prevent this make sure your player resides in the Persistent Level and not a streaming level.