Recently, Google released an update of Android for Nexus 6. Update to 7.1.1 version was strongly awaited, and the initial version of the update had some bugs that were later seemingly eliminated. However, today happened something that nobody expected - Google released again Android in 7.0 version and version 7.1.1 officially disappeared from the servers.
How says Google in official announcement, reason is quite simple - the update caused some problems in system (mainly in Google Pay option), which Google hasn't solved yet. To go back to the system in 7.0 version we should use the OTA update, and in case of problems it's necessary to do factory reset of the Nexus 6. We don't know whether Google is planning to release a new update for Nexus 6, or Android will remain officially in the version 7.0 for this phone.