Critical! Login does not work in front end!

J1.6.1+CB1.4
Sometimes if user inputs login data through CB login, there is no actual log-in process.
But in backend he is shown as logged in.
The second time I have such a bug. It elimminates some time later itself.
I used different browser on different computers. The problem occurs for specific users. If some other logs-in it is ok. Maybe problem with inside session time of something like this?

Problem is solved if I reset (the same password) the password for the user from back-end!!!! But if user has such a problem he would be misleaded and would not notificate admin.

Trying to understand correctly. If you login it sometimes will fail and the only way to finally get in is to restore your password via forgot login then re-attempt to login? Could you please provide steps to duplicate your issue so may investigate further. Have not had any failed logins to J1.6.

Not so exactly.
1)User logged-in some time ago (so in backend I see that he is online)
2)After some minutes, he cannot log-in from front end
3)To restore his ability to log-in I have to go to the back end and reset the password (actually the same therefore there is no reason to suppose that password was changed)
Now the problem is resolved by 3) and no opportunity to repeat it. If it would occur again I would PM you.

Don't understand, why would he need to login if he's already logged in. I can't duplicate your issue. Please ensure you're using CBs login module and no other.

I know it seems misleading but actually it was a case a couple of times. I would notify you and make screen movie next time the problem would appear if any. Thank you.