Go here. Have a support agent call you. I have a dead Nexus 9 on my desk from the same issue (got a Nexus 6 OTA pushed to it) and all I did to try and fix it was flash the right build.
EDIT:
Scratch that, because NRD90M was a Nexus 6P build. It's the one that was pulled because of issues with certain carriers.
All phones running it should have been updated to at least NRD90U by October 11. Not sure what the problem is, and you may have to flash a newer build yourself with one of Google's OTA files.
Leaving the above information in case anyone stumbles here from a search, because it can be a real thing.