Multiple clients are installed, but the server just sees one of them only.

TeamRenderServer or Cinema 4D sees just one client, despite multiple clients should be available.

Cause:
As every client does create a unique ID at first start inside the preferences folder of the client, this can happen, if you cloned a whole computers data or partition.
Now all clients do have the same ID and the server does see just one of them.

Solution:
After installing and updating the client and prior cloning, please delete the preferences folder.
You can find the folder through the preferences inside the program itself, using the button "Open Preferences Folder..." on the bottom.

Alternatively you can just copy the Cinema 4D/TeamRenderClients installation folder to the other machines instead of cloning entire computers/partitions.