I just went through the upgrade process from 2.7.2 to 2.10.3. Now when I try to login, the login page just refreshes. I've tried different browsers and restarting browsers. No error messages, just a page refresh. Anyone else run into this?
Assuming cookies and my MSM query above fails you, perhaps review some of the comments on this bug report : https://support.ellislab.com/bugs/detail/19334
It's for older versions but there's a few nuggets that will help you. For instance some people report login issues using Zoo Flexible Admin or Republic Analytics which are both extensions.
Also (from the link), might be worth searching your third_party directory or your exp_extensions table for extensions using the
cp_member_login hook, will help you identify the culprit as you commented that disabling extensions fixed things up nicely...
Also, check our session domain and/or perhaps try juggling the Admin CP session type and check your
Though, as you state it's probably down to an extension using the CP hook that is incompatible or something, just need to locate the offender. Let us know how you fare!