UPDATE: It turns out these were swarm cells and half of these bees swarmed on Aug 7. I didn’t expect them to swarm this late in the season, but I guess the swarm instinct was strong.
Yesterday, I inspected my top bar hive. It had been a week and a half since I last visited them. The colony is doing excellent aside from some slight cross combing that is happening at the back, in the honeycomb. The queen is definitely very active and thorough with a great laying pattern and signs of brood in all stages of development.
However, on three of the bars that I examined, I found open supersedure cells like the ones pictured above. They caught me a bit by surprise and I’m not sure why they’re there. I believe I saw at least one larva inside these cells, but it was very difficult to see inside.
I don’t want to remove them, because I trust that the bees know what they’re doing better than I do. Perhaps the queen is maimed or very old. Otherwise, this is an extremely healthy colony. Perhaps these are just empty cells to be used in case of an emergency.