dangorham
Check all possible logs (general server logs, webserver error logs, PHP error logs, MySQL/MariaDB error logs, osTicket System Logs, Browser Console logs, etc.) for any related errors. If you can access the login page but can't login then that either means you are not an Admin (only Admins can login during Upgrade Pending state) or likely your Agent account is limited to an external authentication source which will likely not work as your system isn't upgraded yet. You will need to go to the db, go to the _staff table, and set your backend
to NULL
so you can login using your local osTicket password. If you don't have a local password you will need to set one using a bcrypt hash using 8 rounds of entropy. There are many free sites online that can generate one for you.
In case you haven't seen it, we do have Upgrade Documentation here:
Cheers.