Hope your Output Messenger client is connected with Server & you are able to view other users in your User List.
1. Check Restrictions : In Server Manager, we can restrict communication between each group. Make sure your group is not denied for other users.
2. Client Side Filter : Make sure your colleague has not hide you or your group in Settings > Display Details > Hide Users/Groups
3. Check License: If you are registered user, for a 20 User License, maximum of 20 users will be displayed online. Other users will stay offline, even they have connected with Server
4. Check Client Version : Better to have same client version for all the users in your network.
Hope this helps.
