Oh hey,
The three footprint problem is a known issue a lot of us are experiencing, unfortunately. ): Hopefully they'll get that fixed again soon so that we can all go back to accurately tracking down that Pokémon we want.
Other than that, did you try reloading your app? If you were walking with someone and they were seeing Pokémon in the same areas, I have to imagine your phone wasn't fully communicating with GO. That happens to me from time to time; I can't tell you how many times I've bad to restart the app... there are odd hiccups right now.