Short description:
The side quest "Settlers Shortage" tells you to "Apply 5 Traveller Families to the Mayor's House, but applying a Traveller Family doesn't register.
Screenshot:
Possible cause:
You are trying to apply 1 Traveller Family (=5 Settlers), instead of 5 in 1 stack (=25 Settlers)
Prevention:
Unknown
Workaround:
Produce 5 Traveller Families as 1 stack (=25 Settlers) in your Provision House and when it's done apply that to your Mayor's House.
Related:
Original thread(s): 1