Hi Tonia,
I think we'll need to gather some site specific information to try and identify why these interfaces are not being displayed. Some things that immediate spring to mind is if those devices are on a different subnet that may not be allowing SNMP data through. Or the devices themselves are not able to supply SNMP data (we could try to perform a basic SNMP walk to test/validate). I see you've already logged a case to report this, which is probably the best way to investigate this behaviour in more detail.
Regards,
Scott