I have a minecraft world from ~2016 and is evidenced by the old styled villages and yesterday I opened the world again all entities dissapeared, only item frames didn't, this included villagers, wolves, horses, minecarts and even paintings! I don't know why this happened and even though I don't play that often that world holds a very important value for me

Here's a log like of the things that I did 

20-Nov- I opened the world again after some months of inactivity, my friend logged in too and we opened some new nether portals to explore some new 1.17 chunks
22-Nov- I opened the world, my friend tried to log in but couldn't so I mined some deepslate
29-Nov- We both logged in and after colecting some final materials we tried to go back to our home base, we got into the wrong portal so we came back to the nether and got the right one and when the world loaded we noticed ALL of the entities were missing because the sheeps from our sheep farm were missing and the horses we had to travel, and upon further inspection ALL of the old entities were just gone, no drops, just dissapeared

I hope this has a fix and I will attach some images of the missing entities

P.S: My native language is spanish so that's why the signs and coordinates are in that language