J3.x:Unable to login with 2fa enabled after 3.6.3
From Joomla! Documentation
There are issues if you have a Joomla! website with 2FA enabled.
After updating to Joomla! 3.6.3 and relogin with 2FA, you may have an error message: Must match character set and you can't login. (see: https://github.com/joomla/joomla-cms/issues/12458)
This pertains only to Joomla! version(s): 3.6.3
What is the cause
It looks like there is an issue with a third party software (FOF) distributed with the core Joomla! package.
How to fix
You can login with any user just without filling the 2FA field also with a account that have 2FA enabled. The other steps are not needed any more.
Login with a User account that did not have 2FA enabled and disable the 2FA Plugins
Login via FTP to the website and rename the folder JROOT/plugins/twofactorauth