Unbound can only follow the default route or server-specific routes in the routing table (if you have forwarders setup). It doesn't know about active or inactive WANs.
If you are in forwarding mode with multiple servers configured and some using each WAN, then it is normal for unbound to query them all. Again, it doesn't know about active or inactive WANs, it just queries the forwarders and tracks their quality at all times.
If you are in non-forwarding mode, then you may want to change the option under System > Routing so the default gateway follows your chosen gateway group.