Issue:
After setting up the client PCs to connect to the EndPoint Manager, only one PC connects at a time.

Cause:
Each client install generates a unique machine identifier (machine ID) that the EndPoint Manager uses to identify the clients attempting to connect to it. 
The machine ID is based on the hard drive serial number. 

There are real-world instances that the hard drive serial number is the same on individual hardware. Or the master image used to deploy Windows on multiple PCs inherits the hard drive serial number of the master PC.

To check this, open your Command Prompt and run the command below
wmic diskdrive get model,name,serialnumber


Solution:
(1) On some deployment platforms, you can have each deployment instance generate a different hard drive serial number

(2) The other solution would be adding a switch on the setup.ini file for Reboot Restore Rx Pro / RollBack Rx Pro. Do note that this can only be initialized during setup and not afterward

To do this
- from the installer folder, open the setup.ini file (using Notepad)

Anywhere under the "General"  add the getid switch - please try one variable at a time and check the endpoint manager if it works

NOTE: If you are using a custom setup.ini, manually add a [General] section

getid=4 (this will use the MAC ID as the unique identifier) 
getid=6 (this will use the CPU ID as the unique identifier)
getid=0 (the client installer will generate a random number as the identifier) 



- Run setup again once you've saved the changes to the setup.ini file