I am not sure if this is a prevailing problem being posted at the forums. But I can assure you that this is not some sort of conspiracy, or a made up problem for more donuts and coffee. This problem is real and my advise is some kind of silly that should not be counted as “for real”.
1. After following the instruction here, the newly created SuperAdmin password was successfully logged in at the back end.
3. The same password was used to login at the front end– successful!
5. When the superadmin went back to login at the back end (few seconds later), the message came out saying “Incorrect Username, Password. Please try again”.
6. The superadmin account went back to the front end to login, the message came out saying “You have successfully Logged in”.
Conclusion: The superadmin account can login at the frontend but not at the backend.
As stated here: How can I recover my password.
My Advise: (no coffee and donut this time)
What the hell is your SuperAdmin is doing at the frontend where that account can do everything at the backend. For now, don’t use the superadmin at the frontend. Avoid that place if it is giving you the problem.
Time to visit the Joomla! Forum and find if there is a similar problem reported.