I just found out that when exitting game horses ( i didnt see that with other mobs) disappeared
even if mounted. if mounted the game would show my character not mounting a horse but as i was experimenting with that bug i found they would re appear sometimes if i took distance by flying away.. i then came back to the world where my horse disappeared and switched to creative mode to fly away but Simply changing the gamemode made the horse reappear and make me mount it again as if nothing happened.
for me it also affects villagers, but it seems kind of random.. in my case only one ennemy and all villagers diappeared as well as some of my items
I m not sure wether it is intended or not but i ve found that on some occasions raids spawned Inside of the village ( which is surrounded by a 2 blocks tall wall ). I still haven't found the exact point they come from but there isnt any place where the wall can jumped over by any npc. Also the boss bar disappears on death during a raid