Massive Stall when PUN session is being established

I am using PUN in an Android application which is rendering graphics at 60 fps.

I'm connecting using ConnectUsingSettings and JoinOrCreateRoom (in OnJoinedLobby).

At some point during a successful connection process I get a massive stall, which significantly impacts the user's experience.

Is it expected? Is there any way to prevent this stall? Is it known what causes it? How might I approach finding out the cause if it is not expected?

Thanks

Jules