I recently got the newest build of Windows 10 and suddenly my Xbox Music app stopped streaming music from my XBM account. The fix was simple. You’ll need to run PowerShell as an administrator and uninstall the app (you can’t uninstall it any other way.)
Run this (this version name might change with time, so you can get get-appxpackage to search for the app):
Go to the Store and you should be able to reinstall the app from there now. If it doesn’t allow you to reinstall, reboot and it will definitely let you install it from the store then.
You can view a full list of apps in the Powershell by using the command get-appxpackage