I'm currently using 5.7.2 (will be upgrading to 5.7.2.1 here shortly to see if that helps fix any of these problems). I am trying to set it up so that individual users can only edit an individual page. So far I have done this:

Advanced Permissions turned on.
Click the page, click permissions.
Set to assign permissions: manually.
click edit contents.
click add under the included section.
under access click to add user.
click the user i want to add (a registered user).
click save.
spiny wheel forever
nothing changes
click save
see the changes have not been made.

I have also tried to see if this would work if I do groups; it does not work that way either.

So, that is what i have been trying. I'm sure its some setting i'm missing or something I forgot to click, but I thought this would be a very straightforward process like it was in 5.6 ;-; please help haha.