I’ll speak with our developer team and see what they think, I’ve not seen it happen before so I’m a bit lost as to what to advise. I would say the first thing to do would be to check the error report on the hosting account to see if anything has been registered, and deactivate the plugins via ftp remotely – by changing the name of the plugin folder temporarily to something like plugins-old – to see if you’re able to access again.
There’s also a possibility your wp-login.php could have been corrupted. I would say it’s worth downloading a fresh copy of WP from wp.org and in your cpanel check the content of the files match what you have and uploading a fresh copy of the wp-login.php file.
Full details of what you seem to be experiencing are listed here on wp.org with some additional solutions – https://codex.wordpress.org/Login_Trouble