User not linked between Joomla and Moodle

Hi Antonio. We are having a strange issue with one user (manually created in Joomla) that does not have the green tick under "Moodle Account" and "Joomdle User" in the Joomdle Users page in Joomla.

The user exists in Moodle with the same username and email as Joomla.

When the user tries to login on the Joomla frontend, they get an error when trying to access Moodle.

Nothing happens when clicking on "Migrate users to Joomdle". When clicking on "Add users to Moodle", it says user already exists.

Would you have any idea what could cause this issue?

I have checked their user data on both Joomla and Moodle databases.

There is no capital in their username on both.
There is one capital letter in their email, but it's identical on both.

This is a very strange issue. The easiest thing is to just delete the account and recreate it, however I think we should first identify what could be causing it in the first place.