I notice that even if a mason is suppose to be able to mine, he doesn’t.
Can you provide a few more details please?
What version of the game are you playing? Have you checked that mining is enabled for the Mason in the Citizen’s UI? Are you sure the mason can path to the mine? Are there already 4 people mining the zone?
I will check again in another game. If I get the same result, I’ll publish more details.