Control Panel Log not showing everything
 

A user was banned and this can be seen as an entry in the log from the banning.php option. Another user was banned and it didn't register in the log.

Why?

Thank you in advance.

Maybe he was automatically banned as result of infraction(s).

This type of ban is normally logged as well under the name of whoever gave the last infraction leading to the ban.
The bigger problem here is that a user has reached and way overpassed the last level (points from infractions), but can't find any evidence of him being banned.