(semi)gamebreaking bug: hearthlings not following commands/orders after a population of 20

workers are sitting idle when there is a half completed house, or when there is another task (and I have all the resourses), or my combat parties are not going to attack/defend/move at all

Steps to reproduce:
none (sorry) this happens randomly and can not be reproduced manually.
except maybe having a population over 20

Expected Results:
hearthlings doing what i tell them

Actual Results:
as described before



(my master blacksmith, dead [in the corner], because workers refused to build a ladder [for 5 min]. i checked durring that 5 minutes, and i did have idle workers, and enough wood.)
the one ladder you see there was to be built to the ground but only that was build before the builder walked away.

Version Number and Mods in use:
no mods
alpha 17 (tell me if thats not enough)

System Information:
processor- Intel® Core™ i5-6200 CPU @ 2.30GHz 2.40 GHz
RAM- 6.00 GB
system- 64-bit OS, x64-based processor

sorry if this has been posted already, but i couldnt find a topic on it.