[Aqua]

The black beast have a tenancy to randomly make you stuck so its hard to determine what causes it though the z layer related things seems like the most logical thing to go with at this moment in time.

That being said, I've experienced this being stuck in a black beast battle at least twice now both have which have been when the fight was initiated both times had been done the same way without much of a difference. I can't really say anything on it happening when joining the fight with a party that already mid battle since I've not personally experience that side of it.