What was the temperature?
Did you spill any sugar syrup in that area? If you are using in-hive feeders, perhaps some is leaking down to the ground. Or maybe some honey is leaking or leaked out when you pulled out some frames?
It could be a farewell party for the drones.
LOL-Farewell Party for the drones!!! Actually, I've been seeing some nice big health drones in this hive but not the other one. They sometimes have a problem getting in but they're around.
Air temp was 55 f when I took the photo's. They've been doing this for over two weeks in the morning, well before I did the last inspection, the hive has two capped mediums loaded with honey, a third they've started building comb on and I haven't fed since the end of April-never had a dearth here and there's 15 acres of blooming Goldenrod, Joe Pye Weed, Aster 300 yards away and tons of small omental garden even closer. They just come out around 7 am and start jumping off the landing board, crawl/fly back up. An hour later, just (a lot) of foragers coming and going for the rest of the day. The hive 3 feet away is just normal flow activity.