My structure of views:
UITableView
UITableViewCell
UIScrollView
CustomView
UIButton
The problem is UIButton doesn\'t wo
None of the answers worked for me, because my problem was that the button was not visible at layout time or something...
FIX:
1) move the button out of the scrollView completely (to be subview of VC's main view).
2) select the button and the element from your contentV you want your button located (in my case: after the last element in conventV)
3) add the necessary constraints (in my case: to be bottom aligned)
4) Add the rest of the constraints for the button.
5) Enjoy.