My villagers, recently tamed wolves, and sheep keep despawning, despite not dying

I've started noticing this problem recently, as I've recently started to make my own village. It was nice, until I maxed out a Farmer and he despawned. Then I named everyone with nametags, and my cartographer, who was also maxed out, also despawned. Now whatever I do, another villager won't take the place of the despawned villagers, just leaving the cartography table and composter to do nothing. On top of this, I recently went out on an adventure to collect some wolves. I was successful, but when I logged out then back in, they were completely gone. I also had this same problem with sheep, who were in an 8x8 pen. If you could please fix this problem, I'd be very grateful.