In my situation home folders were not automagically mounted, but after some deep digging in various logfiles I found the cause: the home folder of the particular user started with a capital letter.
Solved it by making a link to the home folder with the same name, starting with the small variant of the capital.
Another issue that came by: when the home folder size is above its quotum, it does not automount as well, it even causes that the lightdm environment does not log in (it sets you back to typing user-pass).
Solve that by logging in on tty1 (CTRL-ALT-F1), clean up some files, log out and back in on tty7.