Did you try it with the default WordPress theme?
Since I upgraded to the latest Swift version, the "authors" on my blog can't contribute. When they click button for "new post", a blank page appears - i.e. white and blank, not even an error message.
I logged in with their user name I tried myself. Then I tried to delete their profile and add it again, but same problem still remains.
I try to switch their role from "author" to "editor", but same problem still. Not until I changed their role to "administrator", could they open and write a new post.
So I "solved" the problem by having people I don't know as "administrators", so that they can contribute. I would very much like to change their role to "author" again as soon as possible.
Never had this problem with earlier versions of Swift.
No. I didn't dare to change back. Because last time I deactivated Swift, my color settings were gone.
Anyway, my second contributor had the same problem as well. So I really do think it is related to Swift rather than Wordpress..
Swift doesn't interfere with user roles.
It must be some plugin you are using.