We just upgraded to Moodle 3, in a sandbox, and we are not able to authenticate as admins. Log in attempts time out. Any suggestions?
Did you have any authentication plugins enabled? If so what ones?
Can you use your browser console to say what request in particular is timing out?
Good question John.
Is the timeout happening for admins only but not non-admin accounts? Do admin accounts experiencing the timeout have a different authentication plugin than other accounts that don't have the issue?
Is the timeout your typical web browser web-page timeout? Or is the authentication plugin giving some other more informative timeout error message?
Consider having debugging enabled via config.php, try to log in, and see if any helpful error messages show up.
This sounds very similar to https://moodle.org/mod/forum/discuss.php?d=332405
So I would keep an eye on that thread. As I suggested there have you purged the caches post upgrade?