Could you have a look at this, this is driving me up the wall.
Okay, you have 4 hearthlings assigned to mine. You assign a 4x20x4 block to be mined out (a tunnel).
Say you have 3 really close hearthlings, and 1 really far away hearthling. The three start digging right away, then stop… and wait because they were told the other guy would get that one block, then the fourth gets there and they continue on. But now one needs a sandwich, so the other three keep going then stopping and waiting for the sandwich guy to come back and dig his one block he was assigned to.
I would suggest that mining be assigned as a general target destination for a hearthling and that pathing and decision making be done once the hearthling is in the mining zone. Once the hearthling leaves the zone, no further mining decisions calculated or assigned.
Lovin the game though.