I was thinking with Do Not Disturb, it's possible that landline calls might not seem to come through since most people use cellphones these days (and maybe the landline calls are coming from telemarketers or other unknowns). You can set people in your Contacts to be exceptions to DND, and so if landline callers are more likely to not be in your Contacts, that could be a scenario.
Also, services like Scam Shield could potentially block landline calls since their algorithm might be overly restrictive. I had Scam Shield turned on, and it might have blocked a couple of calls from my workplace, so I turned it off. (I think the Pixel Phone app is already really good at identifying spam accurately, so I don't need another service anyway for that.)