Though it is always recommended to have the same features enabled on both the servers, the secondary server will still function with 16 ports and the issues you are seeing is not related to the difference in licensed features.
In a Unity failover system, both the Unity servers use the location and system mailbox that are created on the primary server. These accounts replicate to the secondary server via SQL replication when FCW is run on both the servers. The above accounts that are created on the secondary server when you installed Unity on the secondary server are deleted by the FCW. In your case, I would suspect whether the SQL replication is setup properly. Open SQL Enterprise Manager on the primary server and verify whether SQL replication between the two servers is configured properly. Also, open the Subscribers table on the secondary server and verify whether Unity_ row is present. If not, re-run the wizard again on the primary server and try restarting Unity on the secondary server.