@Brd709 Difficult to know what's causing it. They SHOULD use the sink right next to the toilet. But maybe they like the fancy one upstairs better than the cheap one on the first floor bathroom? :D
I can see the toilet and the sink in the 1rst floor bathroom are technically overlapping. Try putting the sink in that square you're not using below the toilet in the screenshot. Have the sink pointing the same direction as the toilet instead of overlapping. :grey_question:
EDIT: This is what I mean by overlapping. ;)
https://i.imgur.com/f8Eb4gR.png