Eolas,
Per the
NOS L2 Switching Guide, regarding Service VF and native VLAN Classifications, for Untagged traffic you will want to use the configuration on your port
code:switchport trunk native vlan [VLAN_ID] ctag [CV_ID]
no switchport trunk tag native-vlan
There are other options as well using different modes for the switchport i.e. "no-default-native-vlan" mode. I recommend you review the Switching guide in order to decide which method works best, however with the information you have provided, you may just need to adjust the single line of config on the switchport.
I hope this helps.
Mike Morey
Michael Morey
Principal Technical Support Engineer
Extreme Networks