The correct login behavior appears to happen in Chrome for me. Apparently in Brave or Firefox when I follow the obvious "link" to login, it takes me back to the Presonus login page - which it also does in Chrome. The difference seems to be that when I login in Chrome, I'm actually logged in right away, across tabs and browser instances. . In Brave and possibly Firefox, this "system wide" login is less perfected it seems.
A clue that this was happening was when my login status (after I had logged in) went from not logged in to logged in while I did nothing but sit and watch it refresh on the Presonus home screen.