Bee Disappearing

The bees in my minecraft farm keep disappearing after a while.

Relevant details about my farm or situation below:

1. The bees did not sting me
2. There are 2 bee farms. One is a dispenser farm, and the other one has campfire underneath the beehive. For the campfire one, there is a carpet between the campfire and the beehive.
3. The bees are not exposed to water, so there's no possibility of drowning.
4. It's an enclosed farm, so there is no way the bees can get out. There are at least two layers of security (completely enclosed).
5. The disappearing happen on both of my farms.