A speakerphone echo bug introduced by the Android 7.1.1 Nougat update for the Nexus 6 has now been fixed, numerous owners of the 2014 device confirmed on Google's Product Forums. The bug was initially spotted back in January and is seemingly eliminated by the March Android Security Update for the Nexus 6, reports indicate. The latest security patch for the handset had a number of its own issues and Google even pulled it from its distribution channels before resuming its rollout due to an unrelated problem with Android Pay. The initial build of the March Security Update for the Nexus 6 wasn't able to pass the SafetyNet check which consequently prevented Android Pay from functioning. The re-released build seemingly isn't any different to its predecessor but it doesn't have to pass the SafetyNet check since Google disabled it until the issue is resolved.
Following that turn of events and the fact that the latest software update for the Nexus 6 ships with a fix for the aforementioned speakerphone echo bug, the March Security Update currently has no known bugs on the Motorola-made smartphone. The speakerphone issue was seemingly a widespread one, as a significant number of Nexus 6 owners took to Google's online boards to complain about the bug. Following the update to Android 7.1.1 Nougat, users would experience speakerphone echo during calls and the problem was apparently so pronounced that it made speakerphone calls highly inconvenient. While Google has yet to confirm this, it seems that the problem was caused by the microphone of the Nexus 6 seeing how muting the microphone following the 7.1.1 update would remove the echo. Naturally, turning off the microphone during a call isn't a particularly effective method of resolving the issue, so Google had to develop a fix as soon as possible.
The March Security Update for the Nexus 6 that resolves the bug is being rolled out in stages, meaning it may be a while before you receive a notification prompting you to download the package. Anyone who's feeling impatient may try searching for the update manually by opening the Settings app on their Nexus 6 and navigating to the "About device" section of its main menu.