Wither Despawns After Crashing

After hours of killing Wither Skeletons I finally got 3

and I spawned the Wither. After a few minutes of fighting the game starts freezing and I get kicked back to the Phone screen. When I re-Enter (after a multitude of errors you’d think the devs would fix in their own “game fixing update” I find that there is no Wither on the world. Then the game gives be the achievement: The begging. This game is messed up.