Sometimes, you can see a user appearing in the Roster that does not appear as a "User" in ClassGather meaning you cannot access a number of features to troubleshoot with that user. It's entirely likely that users themselves don't notice a difference between whether or not they appear on the "Users" page, but if you are able to impersonate users from ClassGather directly, it can save a great deal of time and energy when troubleshooting issues.
For example, by going to the Roster and searching for the student "Albert" in our system, we can see that this student exists within the SIS database.
However, on the "Users" page under "Settings" in the collapsible menu, we can see that no such student exists within ClassGather.
The most likely reason why this would happen is that Albert simply has not launched into ClassGather directly and has only accessed the information in ClassGather via an LMS or some other external program. As a result, Albert's information is waiting to create an official user in the system.
Luckily, this can be a pretty straightforward fix. The user just needs to login to ClassGather directly. If you link them the login page of ClassGather, there may be a "Login with [LMS]" button. Clicking that while logged into a system integrated with ClassGather, will automatically log the user using the SIS credentials, generating a "User."
Additional notes: Linking any other page instead of linking the login page will also prompt them to login, so you can use that if you'd like.
If this button is not present on your instance, you will need to find another way to troubleshoot the issue.