Villagers despawning when leaving chunk borders

I had two max level villagers, and then I went exploring to find geodes but when I came back they're gone, and later on I went to the nether and same thing happened again. I was playing on peaceful so there's no hostile mobs that cAn hurt them. I walled off the village too so they can be safe inside and won't wander off and fell on some deep hole or caves.