This is possibly too late to be useful but this might be useful it it happens again:
- Can you tell us what exactly what was experienced by users who tried to sign into the site, especially any error messages. Screenshots help communicate what you see (hide anything you don't want to share publicly).
- Are the affected users of the site "manual" users (i.e. internal to Moodle) or are they authenticated by an external service, e.g. Active Directory.
- "Can not generate key-pair" and "Disable login" don't look like Moodle errors. Can you provide exact examples of entries from the logs (again redact any information that you don't want to share publicly).
- Enabling debug messages in config.php may provide additional information with error messages in the browser or in the log files.