I might have a tip for the first one. Dou you have your cows grazing?
Might be in relation with this bug:
If the cows are not in the barn they can’t be slaughtered. So you need to stop grazing (and see if the cows even move in at all) or wait for the winter.
Second one isn’t a thing about population and not “using” a house but about Desirability. If it drops below the needed threshold for upgrading to the current stage they get abandoned after time (maybe a building was destroyed during raids, or you moved one). If this wasn’t the case I think you need to give further information.
And a general point: Nice that so many people report bugs, but I think it would help the devs to post every bug in a single Thread. As the devs stated:
Whenever possible, please post separate bugs in separate threads. If it is a collection of minor/related issues, it is fine to post them together.
This will help them categorize and organize bugs 