(imported comment written by Lee Wei)
One possibility is the use of a “configuration lockdown utility” that prevents changes to or restores the Windows Registry.
TEM stores the ComputerID and some operation data in the Registry.
So if a computer is restarted without the TEM Agent data, the TEM Server will assign a new identify to the Agent.
Please see this thread for more info:
Running BES with Faronic Deep Freeze
I am not familiar with the workarounds and the thread will provide additional info.