Bees wont come out of the hive/nest

The bees will not come out of the hive after they have gone in for the night, been several weeks I can hear them in the hives and nests but they wont come out. I placed down the hives and nests, bred the bees to get more, then they went in because it was getting dark and haven't seen them since. Replaced the hives and nests to make sure they weren't backwards.... nope they're right.