Almost always, the user is simply not assigned to an office and needs to be assigned to an office to show up in these places.
After logging in to the web app, click "Users" within the left hand menu. Click the User's name that is only assigned to either "Department" or "Region" that is not showing up in the app on the user lists.
In the profile, click "Org Assignments" within the options at the top of the profile box.
Click the pencil icon to the far right.
Within the pop up box, click the downward arrow next to department. Click on the appropriate Region drop down (if there are multiple). Click the check box next to "Office," then click "Save."
Please log out and log back in of the app to ensure the application of the organization changes.
NOTE: If there is no drop down next to the Department, please click HERE to learn to add an "Office" to your account.