Troubleshooting frequent intermittent DNS_PROBE_FINISHED_NXDOMAIN ?

[violaDesmondScreenSystems]

Hello,

I'm new to OPNsense. I'm trying to set it up for my home, including a small homelab; but I'm getting intermittent failures with DNS lookup from my Mac desktop, and from my phone via wifi.

When I visit webpages from my desktop (wired connection), many sites return the error DNS_PROBE_FINISHED_NXDOMAIN; it ranges from about 5% to 80% of sites I visit. The percentage increases the longer I'm using the web. If I leave the pages open in my browser, then in general, the pages finally resolve, but it takes anywhere from 2 minutes to an hour.

When I browse with my phone via wifi, I also get errors visiting various sites; I can resolve this on my phone by temporarily disconnecting from wifi, accessing the sites via cellular data, and then re-connecting to wifi; those domains then resolve correctly.

My path is as follows:
 - ISP Router <-> OPNsense 25.7 on a Protectli <-> Netgear managed switch (default settings, no VLANs defined yet) <-> iMac, WAP, other computers, etc

It's unclear to me how best to troubleshoot this. I've searched these forums (and googled widely) for DNS_PROBE_FINISHED_NXDOMAIN, DNS lookup, etc; and have found various suggestions about what my settings should be, which I believe I am following.

Any suggestions for a troubleshooting path?

Thank you.