I have had a Watchguard Firebox x55e since May w/o any issues. Upgraded to their new version 11 OS last Friday.
We have two DNS servers specified for the external interface and have it handling DHCP.
Yesterday morning it started issuing 192.168.137.1 as the primary DNS server and no secondary. That IP address is not only not one of the DNS servers we use but it's also not a machine in our network nor our internal IP range.
If you release and renew the IPs in Windows it will go back and forth from receiving the incorrect DNS server to correct ones.
Everything else is getting set properly via DHCP all the time. This is effecting several desktops and laptops on our network.
I'm in queue for support from Watchguard but they take forever.