Villagers and animals keep despawning

I had experienced some despawning issue of villagers and animal mobs despawning, I even get them in a room and often trade with them to the maxed level, even named some of them but they still keep despawning, I had doubted the stuck in wall problem but I gave them enough room and the bed at the center, I tried changed to the peaceful mode and breed them again but still have the same issue, these problems are getting on my nerves, please fix soon.