Despawning of mobs (cows,sheep,hourses,villigers etc.) 

Tried using name tags which resulted to them despawning also

occurs mostly when logging off and back into the game.

Noticed that any moveable object also is effected not only mobs example
Minecarts, boats, tridents etc. As by these take effect it means of losing progress mobs
Or anything which could be related to giant redstone mechanisms