This problem has been encountered since versions ("1.19.60.X, 1.20.0 - 1.21").

This occurs possible when crafting a banners & Banner shields from 2X2 Crafting, Crafting table.

Relates to MCPE-175116 (First part of performance issues)

Steps to reproduce

This only reproduce with Android

Crafting testing:

Crafting in 2x2 banner shields

Create a new world

Open your inventory with 2x2 crafting, Take 1 Shield to left or right grid

Place a 1 banner to shield ------> The performance is down upon the placing 1 banner

Click the custom banner shield in crafting output -----> Another performance down

Crafting in 3x3 banner

Take Crafting table, Stick and Wools

Open the crafting table and create a banner shown the following recipe -----> The 1 wool filling into 2x3 grid can lead to performance down

Mob Spawning:

Create a new world with Mob spawning is disabled, Start the mob spawning by using /gamerule domobspawing true and Wait for mobs spawning -----> The performance will down upon the mobs spawned.