Mobs Despawning

In my Minecraft Survival World, my animals and my villagers are despawning! I had a pig farm with 20 pigs, and now it has been reduced to 5 pigs. I had 18 villagers in my building I built called “Villager Sanctuary.” It’s doors are iron doors for the exits. Torches light around the whole village. A day before, the villagers breeded to a max 18 with 18 beds. The next day, my master level farmer has despawned. The nitwit also despawned. Currently, even more villagers are despawning leaving with 7 Villagers. In my chicken farm, I have an automatic egg farm. A hopper in a Minecraft runs underneath the chickens to grab eggs and place them in a chest. Suddenly, my hopper in a minecart also despawned!!! Is it because I have too much chickens in my chicken farm?