According to the company’s official statement on the matter, “We were made aware of reports from some users experiencing inconsistencies related to audio playback via third-party apps and SD card encrypted data read performance, after upgrading to Android 7.0, Nougat. We’ve identified the root cause and are aiming to provide corrective firmware and re-commence the rollout as soon as possible.”
Basically it was due to a bug which is why they put the brakes to the update, at least for now. It is unclear as to when the update is expected to resume, but hopefully users won’t have to wait too long for it. In the meantime users who have already updated their eligible Xperia handsets to Nougat, hopefully you won’t run into the issues mentioned above.
If you do we guess you can try to downgrade to the previous build, or wait for Sony to push out the fix and updated version of its firmware.