We have multiple 802.1Q subinterface on Cisco Switches. The primary interface is showing the traffic but the subinterfaces don't show the traffic.
On the effected node's summary page, from the management widget, click 'List Resources', and locate the sub-interface in question, click the arrow to the left of it's name and confirm that the three statistics (or only the ones you are interested in!) are checked. Hit submit to confirm the changes or cancel if no changes were made.
If these were already checked, and you've confirmed via the CLI that traffic is indeed passing over the sub-interface, then you have a couple of things you can check:
Let us know how you get on. If you're seeing good stats for all other interfaces, my suspicions would be down to the SNMP user's access.Note that I have assumed you're using SNMPv3 here. If not, try switching to SNMPv3, with a user which has sufficient access, and see how you get on.