Perfect, that did the trick.
I was aware the Network Services Filter was for WAN only, but just added here in the rare instance that could be related to the forwards (I know, unlikely, and seems silly now thinking of it).
Thank you so much for the help!
Right now I have in my network my router and a RPi running Pihole + Unbound which is my DNS resolver.
I believe I have disabled all router DNS forwarding settings, but it still keeps port 53 open (no 853) and any queries sent to the router are then forwarded and resolved by the RPi. While not a...