Few months ago, Google announced Android 7.1.2 update for selected Nexus and Pixel devices and you may have noticed that the Nexus 6 and Nexus 9 were both not listed because Google won't be pushing further system updates to these devices.
Google guarantees Android system update for two years, so Android 7.1.1 is marked the end for the Nexus 6 and Nexus 9. Now, Some Nexus 6 users on reddit are now receiving Android 7.0 OTA on top of Android 7.1.1 Nougat, Sounds weird? Here's the proof-
After Android 7.0
Phone app and acore keep force closing to the point to where the phone is unusable, I managed to make it to Update in settings and it shows a 56.1 Mb update for March security patches but the spam force closing won't let it. Gonna have to side load from the images on Google's site. - reddit user B_Stache
That said, if you have downgraded/updated your Nexus 6 to 7.0 via OTA, you should sideload Android 7.1.1 Image right away. Google has yet to announce anything official on the matterSource: Reddit
There was a recent OTA update for Android 7.0 that is causing confusion for some Nexus 6 users. For those of you that want to guarantee future OTA updates, you will need to get back on the 7.0 supported track. If you are experiencing issues after accepting the 7.0 update, please factory reset your device to help resolve any problems.
For any Nexus 6 users that want to continue flashing/sideloading future builds, you can stay on 7.1.1 and continue to do so.