I seem to have the same sort of problem only with fewer setbacks.
I migrated my wordpress installation from /site/ to root. I changed my sites URL through the admin panel.
Now the wp-admin login seems bugged. I cannot login with my credentials ( when I try to, the page reloads with no error ). Then when I reset my password, it DOES let me login with the new password. Only once.. after I logout again I have to reset the pass again to login. Very annoying..