E.g. Ć or ź. Reported it before but still not fixed, had to change password… No clue why there would be validation for password inputs on log in form in the 1st place.

Thanks for reporting this, and sorry for the confusion.
Passwords currently support ASCII characters only, so accented or non-Latin characters aren’t allowed. We understand this wasn’t clearly communicated during login, and we’ll work on improving the validation and messaging.
As a workaround, you can reset your password using supported characters here: https://fuze.io/login/reset-pw/