to sum up what happens, I order them to build me a house: they start, then they either go to bed or eat lunch, and after they do that, they don’t continue and finish it.
this is an ACTIVE BUG
Try clicking Build & Design, clicking on the house’s blueprint, and press start building again. It usually works for me.
Already tried. I also tried restarting the game but it didn’t work either.
Thanks though! ^^
Your welcome! 
Team Radiant will probably fix this bug at some point.