Michael,
Check and see if the hard drive is filling up on these endpoints. There is a known issue for the 11.6.3 and 12.0.1 agents where if HTTPS is enabled with IE, it will fill up the HD.
Also for those 6 agents, what are they doing. Is there a similar application ar use that they have? It also might be that those 6 agents are showing the HD as a USB device and as a result are inspecting every write to the drive. Since you have the removable storage turned on.
You should run the DeviceID application (Endpoint Tools folder) and run it on those agents. See if the local drive is actually considered an USB device.
Hope this makes sense.
If this solves your questions please marked as solved.
Ronak