When Microsoft released Windows Phone 8.1 for developers one of the apps that was most underdeveloped was the Xbox Music app. The music features had been split out into a separate app rather than part of the OS and at launch the app was a little rough around the edges.
Today Microsoft have updated the app improving the performance and reliability of the app. Hopefully this should improve the speed of the app as well as reducing the app crashes.
You can find the app in the Windows Phone Store.