Don't think I've seen this problem before. Have you tried to log in with a different account and see if it still doesn't go through?
It could be numerous things TBH. Maybe a conflict with something you installed in Cydia. Maybe it's a jb bug like you said. Or it could just be your phone being uncooperative.
If it were me...I'd do a restore and rejb. If you've got SHSHs saved maybe consider doing so if you don't find anything wrong with Cydia stuff you might've installed that could be causing conflict. Or trying another account.