On build OPM1.171019.011 of Pixel 2, the phone is recognized as ARCore compatible, but no matter where the crosshairs are placed, they never turn green to allow tracking. This issue appears to be resolved with build OPM1.171019.013, but is still an issue with that build installed. This issue was discovered using the SDK Examples, specifically 3D Model Instant Tracking.
could you check if the same behaviour can be observed with the ARCore sample app from their GitHub page?
I would expect the ARCore sample app to never be able to find a plane.