Kicked back to the home screen every time

My daughter gets kicked out of the app and back to the home screen whenever she logs into the app. Anyone else had this or know what’s going on?

Something like this happens to me when I switch between apps. When I choose again PoGo after doing something else (like Whatsapp), then PoGo restarts from the home screen. But once it has started, it works fine.
So, it’s not the same, but maybe it gives a hint.