if I deactivate Buddypress, issue persists. I am totally lost here.
the strange thing alse is that the log-in page is has the wordpress logo, is this correct?
Regarding #2: I do not have many pluggins but followed your suggestions, I have deactivated all the pluggins and have also used 2017 theme, but the result is the same.
The username is recognized, the problem is with the password. Even resetting the password through Dashboard/users/reset password, doesn’t work. Allways the message is the same (Oops, that’s not the right password. Please try again!)