From the update diary, I ackonwledged that rules of creature spawn were changed to be more like Java edition. I remember that Java edition spawn hostile creatures in a radius of 24-32 blocks, freeze them in 32-128 and clear them whenever they are out of 128 blocks immidiately.

So, why mobs in BE disappear when they are out of 54 blocks? BE should have a bigger area to hold those creatures. The screenshot shows a slime farm I created in survival mode, from the structure block I see, slimes jump off the edge and diappear at the second layer(with red circle).

This feature is killing some technological players, especially for those server players who have built some big farms to gather resources. I sincerely hope you can consider my suggestion and adjust the disappear area as big as JE. It would be highly appreciate by some technological players like me.