Hi,
I started seeing this problem since 1.16.101 was added to the game.
The game become very lagy and basic jobs like eating and drinking potions takes many seconds and mobs become very slow like they are in in space and furnaces takes to long to cook and smelt thing ( and yes i checked my random tickspeed it 1 the default nothing is wrong with it) blocks textures are louding and disappearing in the wrong time (one time I found a a spider spawner and a buried treasure because I can see throw blocks) plus all the problems you have mention before.
My device is :Samsung j4 core
1gb ram
Android 8.1.0
I know my phone is a low end device but minecraft was running just fine in 1.16.40 (that doesn't mean that 1.16.40 was perfect )
This exact bug happened to me after I used the plastic texture pack then deactivated it .
For some reason some of the textures from this pack stayed after i removed it like the chat button and the Enchantment texture breaks helmets, chestplates, boots, tridents, crossbows and xp bottles and makes bows and leggings invisible.
btw i play at the latest version 1.20.30 i have no add-ones and no texture pack and i try deleting and re-installing minecraft