Downgrade required 'to guarantee future OTA updates.'
The Android 7.1.1 Nougat update for the Nexus 6 hasn't gone entirely smoothly so far, with the most recent March 2017 security patch breaking Android Pay on the device. And now in another bizarre development, Nexus 6 owners who updated to 7.1.1 are seeing an over-the-air update back to Android 7.0. Worse still, some are reporting that the downgrade back to 7.0 has caused issues with apps upon completion.
Over on Reddit, a Nexus community manager — listed a verified Googler on the side — said that the move was made "to guarantee future OTA updates."
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.
It's not clear whether this means all updates for the N6 will be based on Android 7.0 from here onwards, or whether there'll be another 7.1.1 push at some point in the future. The second paragraph suggests more 7.1.1 builds will be forthcoming, though perhaps only available via sideload. It's also not clear why the OS downgrade itself is necessary, but it's possible it has to do with the March 2017 OTA breaking Android's SafetyNet functionality, which was the root cause of the problems with Android Pay in that build.
The Motorola-built Nexus 6, released in late 2014, is no longer supported for OS updates beyond 7.1.1, and so future builds (whichever number they carry) will just include new security patch levels.
In the meantime, Nexus 6 owners are left in the unenviable position of having to decide whether to take an OTA which not only downgrades them to an older OS, but which may also break some apps when it's done.