everything except the animals i have tamed... despawned???

i have no clue man?? i had mending villagers and all that nice stuff and they despawned. not only them the other villagers i had in a cage near by did too AND OTHER VILLAGERS I HAD IN A DIFFERENT CAVE DESPAWNED TOO. AND THE VILLAGERS AT MY IRON FARM. 
AND THE ZOMBIES ON MY IRON FARM.

what happened? my zombies escaped out of this 2x2 area with a roof and everything at the same time??? and my villagers all escaped at the same time??? what happened im genuinely so confused and a bit mad? because i just beat the dragon, got my elytra and completed my creeper farm.

 

the one thing that didnt despawn are my cats i tamed? i dont know what to do pls help