I am also having a similar problem. When a user updates their profile, their user level reverts to NULL (I can see this is phpmyadmin). The user level row is not visible to the user, it's in a "show region" for administrators.
I have followed all the steps above but when adding the code
<pre><?php @session_start(); var_dump($_SESSION); ?></pre>
to the Log In page and updating the profile, I still get "NULL" output at the head of the log-in page.