the first issue is serval in-game items no longer use data and have separate ids 
2nd buckets no longer have nbt or its read only

fall damage is now server-sided and 

npcs cannot have more then 30 kilobytes of data

npcs with forced data beyond 30 kilobytes lose their data

addons that require experimental gameplay cannot be added to realms and worlds with said pack will fail to upload following another error

resource fallback mode removes aspects of behaviour packs example functions

when client-sided may fly = true it appears to others players as the player was super jumping and not flying thereby invoking fall damage to the player

unable to use unused data for spawn eggs using 3rd party edits example
giving the spawn egg data for mob id 65 that witch would make the egg spawn tnt

beehives and beenest do not work in the night or rain

having 2 of a unstackable item makes the item stuck on your inventory

kick command on realms does not prohibit joining

caves and clifts experimental options does not change the hight limit and breaks generation near bedrock

mountains trying to generate past y =256

enderman geometry messed up

custom bioms being litterd with update game blocks after remove packs

when deleting a folder in appdata worlds still appear intill game restart with fallback texture aka error or unknown

settings -> profile -> only allow trusted skins is turned on without users consent modded skins still create lag even the they are not rendering it might aswell make false the defualt

live stream API for most game detect software sees the game as Minecraft java not bedrock edition

rtx lighting leak when entering a lit room after being in a simi lit dark room