I have 5 beehives lined up above 5 campfires directly under them with a glass wall behind the row of fireplaces and beehives in addition to this I have trapdoors stopping the bees from going into the fire. The bees will not come out of the hives on their own. I used a silk touch pickaxe to collect each of them which formed 3 separate stacks so they did not de spawn or something (their is a varying number of bees in their beehives thus the separate stacks). I’ve heard others having this problem when the bee update first came out but, it is now occurring in the 1.16 beta.