There is a bug on singleplayer worlds in 1.16.210. This bug only affects Amazon Kindle devices. When I go into my singleplayer world I have a lot of world lag. My player is not affected by the lag, only the world. When I try to enter any world, it takes at least 5 minutes (it only took 1 minute in 1.16.201). When I place blocks, they disappear after a couple seconds and the items come back into my inventory. Sometimes I am able to place blocks, but they take a long time to update. I place lava and it flowed a block every 5 minutes. I placed sand that should have fallen but fell 5 minutes later. It even takes 20 seconds for items selected form inventory to appear in the hotbar. I have tried playing on different kindle profiles using a different app but this still happens. I even got my memory down form 50% to 40%, but still lag. Luckily, there is not lag when playing on servers.

To reproduce: Play Minecraft on any Amazon Kindle device. Go into a world and see the lag immediately. Try placing blocks and they disappear. Then try placing lava and it will not flow until a couple minutes later.

Note: This bug has only been happening since 1.16.210.