I have many bees is my base, but I don't know why but they just disapear including the ones that are caged in a dome so they couldn't die. I think that is important to solve this problem because it is very annoying that you build your proyects and farms with bees and then you have to refill them with new bees every time. This problem is very critical I guess because the desapearing of the mob could cause the people to stop using the bees and their mechanics just because they are despawning 

(And as an aditional its a little bit annoying that they get stuck in fences 😅)