Existing user not visible when trying to add him to a ring group

Scenario 1

1. Login to Admin Console, click on Ring Groups and on the right side, click on the pencil to edit. 
2. In the Members section, search for a user to add, but there will be no results. 
3. Look under the Basic information section at the site name.
4. Go back on the home screen, click on Users and look for the user in question on what site it is. 
5. Go back on the home screen, click on Sites, and click to edit the site where the Ring group is and the site where the user is. Observe these are on different PBXs.
6. Create the user on the same PBX as the ring group and you should be able to add the user to the ring group.

Scenario 2

If your user is on the same pbx, however, it has been migrated from Legacy to X series

1. Login to Admin Console
2. Edit the user profile that is not visible in the drown Members down the list of your Ring Group
3. Make a trivial change to any field, save, and remove the change if needed

The Extension should now be visible in the Ring Group's Members drop-down list.