In LMS 4.2 (MDL-77306) additional registration data was added. This is included the "primary" authentication type for a site. In this case primary means the authentication type that the largest number of users in a site use to authenticate. (The actual number of users isn't sent)

Looking at the data reported to the site registration database, it is possible that the sites are reporting their primary authentication type incorrectly.

This should be investigated and fixed if there is an error.

See: https://github.com/moodle/moodle/blob/main/lib/classes/hub/registration.php#L200