Game restarts after lock screen

Hi!

Since last or second last update of the game, it often happens, that after I unlock the screen of my Android phone (Oneplus 3T), I cannot just continue with the game like before.
Instead the screen is white, turns into black and the game obviously has to restart. Like a crash.
Fortunately my game doesn’t crash while playing, but nonetheless it could be an indication of a severe bug.

Best regards