The latest System Update for Xbox One is now available to download. The update includes a variety of fixes (detailed below) and will be automatically installed by those using the "Instant On" feature - those who don't use it will be required to download and apply the update after December 12, 2.00 am PT.
According to Major Nelson the update addresses the following issue (and further support can be found here):
Addresses SmartGlass issues for some users when coming in and out of connected standby
Addresses multiplayer issues for some users when re-joining games
Addresses issues with inconsistent notifications for some users
Addresses dashboard performance for some users
Offers improvements for Xbox One's TV, system update, and content update services for scaling over time
Updated wireless networking driver to improve connectivity issues for some users