When the wither goes to its second stage in bedrock edition, it now goes down and destroys a 5x5 chunk of the world down to a very low layer and breaks a ton of blocks and has the chance to either lag out the game or crash it with the amount of block entity’s on the ground. I apologize for the choppyness of the video as it is on the switch and it can only handle so much 

please get this fixed as soon as you can, killing the wither is now basically impossible  for us.