Our Comcast DNS keeps going in and out too, not clear if it is related or knock on effect or something else entirely.
Do you use your car’s built in navigation function — that you paid for — or do you plug your phone in and use its free Google Maps or Apple Maps to navigate?
That the client information doesn't get lost when it goes through different resolvers the DNS extension EDNS Client Subnet (ECS) was invented.
https://en.wikipedia.org/wiki/EDNS_Client_Subnet
explains it better than me. The whole point of the extension is to make geo-guessing the original client over DNS more stable.
Now you can have privacy conscious DNS servers that strip the ECS information (or mess with it somehow) and instead of the server closest to you you get the global fallback for example. (controld.com goes as far to say "switch countries without a VPN" by only messing with ECS. No idea how stable that is though.)
I could work around that by configuring the gateway as just a modem and provide my own router and wifi, but then there are data caps.