Hi Brawn,
There are a couple of different possibilities. One is that a specific set of definitions has been configured by policy for that client group! It's more likely, though, that the SEPM is (for one reason or another) not offering up what the SEP clients are looking for.
Prachand is correct that a bit more info is needed--- the log.liveupdate from an affected client will be very useful. It is also important to know what specific defs are not updating - AV? PTP? Everything?
Also: do these clients retrieve directly from the SEPM, or from a GUP, or from an internal LiveUpdate Administrator 2.x server on the network-?
As there have been many improvements over recent versions, it will also be important to know the version of SEP on the SEPM and the SEP client- can that info be supplied?
Also: check out the LU status on the SEPM- what exact versions of definitions is it making available to clients?
What that info in hand, the community members can likely steer you in the right direction.
Thanks and best regards,
Mick