What nest?

[lotusbell]

For the past few weeks, I've noticed a number of creatures flying in an out if the gaps in the wall in our garden. It's the wall of next doors kitchen/utility room but the wall is on our side of the yard, if that makes sense. I haven't told them yet but struggling to identify what sort of insects they are. Can anyone help me from these 2 photos? Struggling to get a good photo if it. There are only 4 or 5 at any one time.

[NanTheWiser]

Red mason bee - www.bumblebeeconservation.org/redmasonbee/

[lotusbell]

Thanks, I'll leave it well alone I think!