I think I see the cuase of the problem, the 8 computers that are showing in the Ungrouped Clients area all had different names to start with and were then moved to a different location and subsequently had their computer name changed, but Malwarebytes didn't update the existing record, instead creating a new record (so each computer has two records, old and new name).
Original Computer Name: DT-DS2-07A
Renamed To: DT-DS2-07
Malwarebytes shows both devices, but the original computer name shows as unregistered in the correct AD Folder, where the replacement name shows only in ungrouped clients.
The IP Address show in the console matches that of the computer in DHCP, aling with the MAC Address.
A couple of the computers have only just been renamed\re-imaged, the rest have probably been there for a couple of months now.