Not sure if it's mentioned above, but I had similar issue with using my PiHole and AdGuard Home DNS servers with Merlin/YazFi and Guest Networks.
The problem was that the Guest Network had "Access Intranet" DISABLED and therefore could not access the local DNS servers I had set up. Switched it to ENABLED and all works.
Before this,... I wasted a lot of time troubleshooting, rebuilding DNS servers, etc,... this was the only place that hinted about enabling the local network to give access to DNS. Should have been obvious.
Thanks!
The problem was that the Guest Network had "Access Intranet" DISABLED and therefore could not access the local DNS servers I had set up. Switched it to ENABLED and all works.
Before this,... I wasted a lot of time troubleshooting, rebuilding DNS servers, etc,... this was the only place that hinted about enabling the local network to give access to DNS. Should have been obvious.
Thanks!