Computers Don't Show in Contacts List After msi Deployment

We deploy the Teamviewer 12 msi via Group Policy across 9 different sites. At most of the sites, Teamviewer installs without a problem and automatically joins the computer to the group named after the site location.

At a couple of sites Teamviewer installs successfully but doesn't show in any of the Groups or under the Computers & Contacts list. This means someone has to physically go to the remote site and add the computer to the group until I can figure out what's wrong.

Does anyone know why they wouldn't show in the contacts list?

Many thanks