Windows 2008 R2 hosts can't see all tape drives on ESL 712e

[OFC_EDM]

I have an ESL712e.

Have zoned 7 Windows hosts (2008 R2) to see the robotic arm and all 6 LTO5 FC drives in the library.

From the SAN side all hosts have full access to the Port WWN's of the ESL devices.

In CommandView TL all WWN's of the hosts have access to ALL the tape drives and the Robotic Arm.

On the hosts the Robotic Arm shows up in Device Manager in the "Medium Changer" group.

The tape drives show up in the "Tape Drives" group.

From Device Manager on the OS
-----------------------------------
5 of the hosts see the Arm and ALL 6 drives.
2 hosts see the Arm and only 5 of the drives.
It's not the same drive missing for each host.

From a SAN perspective the ARM and 3 drives are on one Fabric (ODD).
The other 3 drives are on the other fabric (EVEN).

I have a case open with HP on this and the first level support could not find any issue with our Zoning.

The host access seems fine in CommandView TL.

My question is...is there anything else that could be causing this behaviour?