I was driving on a highway using Apple Maps for navigation, and it suddenly rerouted me because it thought I was on a surface street parallel to the highway. Then, for several miles, it kept rerouting me back to the highway I was already on. So I canceled the route, killed the app, and set the destination again with no change. I switched to Google Maps, and it did the same thing.
Next, I restarted the phone, and the problem continued with both apps. At this point, I wondered if there was a hardware or even satellite issue. I know nothing about either, so it could be!
I gave up and continued until I went on another highway and tried again. Same thing. This area was more rural, so I had to chuckle as maps traced my route perpendicularly across streets on a non-existent road, like I was an airplane flying a hundred yards to my west. I tried to take a screenshot by pressing the side button and volume, but I accidentally triggered Siri (holding down the side button). When I canceled Siri, Maps rerouted, and the problem was gone. Perhaps a coincidence, but what happened?