I am suspecting scouts.
As an alternative to completely sealing it maybe put an escape cone on it, if there are bees in the wall they will come out (in large numbers) but if there are scouts there will not be a lot on the cone and they will become disinterested when they can no longer get into the hole.
As an alternative to completely sealing it maybe put an escape cone on it, if there are bees in the wall they will come out (in large numbers) but if there are scouts there will not be a lot on the cone and they will become disinterested when they can no longer get into the hole.