I'd encourage anyone with the know how to look into the proximity sensor, as Google still hasn't managed to fix it's sensitivity issue on the Nexus 6, resulting in the exact same behavior as being experienced on Pixel devices, except the screen stays black and only a hard reset will fix it.
There was an XDA user that released a patch for the Nexus 6 on Lollipop that maxed out the proximity sensor's sensitivity, however it was never updated for Nougat and Google still hasn't bothered to fix the code or employ the same tactic the aforementioned dev on XDA did.
Due to the fact the proximity sensor's code has still not been patched by Google to fully eliminate the issue as of 7.0.0 [NBD91U; 12/16], there's a good chance Google devs didn't bother to properly address the issue on the Pixels either.