I had the same thing happen with all 3 of my hives today, I was sitting watching them then they all boiled out of their hives and were in the air comming and going but mostly flying right around the hives in very large numbers.
And about 45 minutes later all the action died down to normal hive come and go. No swarms thou I inspected all the hives after this unusual activity and all was normal.
I was sitting in my lawn chair watching them when this happened and it was cool bees were everywhere up to 100 feet in the air when I looked up.
If it isn't broken, don't try to fix it. If you build it, they will fill it.