WAN1 is a public range, I have a /28 addressable subnet. One of the IPs is statically assigned to the pfSense, one is the modem/router itself (default gateway) and a couple of the remaining ones are assigned to devices sitting "outside" the firewall - these are the ones I tested DNS lookups from whenever I get timeouts from pfSense itself.
WAN2 is slightly different, I get an RFC1918 address, but have a 1:1 NAT set so I can configure port forwarding etc on the pfSense directly. No other devices between that modem/router and the pfSense WAN port.
However, as I mentioned above, I disabled WAN2 altogether last time I saw the issue, and it was still happening after that, all the while DNS queries outside the pfSense were fine.
I'll try your suggestion of running a packet capture on pfSense next time this happens, and will report back…
Thanks.
-Alex