Microstoft's post has it as a known issue, with a solution (I haven't updated yet so no first hand experience with the issue or fix):
IMPORTANT NOTE: Xbox sign-ins may fail, as well, as a result of service host separation. To fix this issue:
Run the following from an admin Command Prompt (or edit the registry accordingly):REG ADD HKLM\SYSTEM\CurrentControlSet\Services\XblAuthManager /v SvcHostSplitDisable /t REG_DWORD /d 1 /f
Reboot the system, so that XblAuthManager now shares a service host process with Windows Update and Background Intelligent Transfer Service.
