As a Pokemon battle progresses, it is possible that after a Pokemon uses a move that Pokemon will begin to fly upwards and remain floating in the sky. When the battle ends the Pokemon will fall back down and die from fall damage. This is particularly annoying if engaged with a legendary and you need to run to grab something. I have experienced this in both the overworld and Ultra Space, though in space they fall so slowly that you can re-engage the Pokemon as it descends to spare its life.

Marking this ticket as Expired because of age and being unable to reproduce the ticket in 7.3.1, if this is still occurring in 7.3.1 please make a new ticket