missing Ethernet in SG 230

We have 2 SG230 with both eth0 up to eth5 (HArdware)

However - we can only assing 5 ethernet interfaces to acutal interfaces (eg WAN, DMZ, internal, external, test).

If I try to create another interface - the "Hardware" selection is empty.

This is the same for both SG230 we have (not in HA of course, both standalone)