Many people have been reporting problems with the updated iOS 5 Music App. The app continuously freezes, crashes, and even restarts the entire iPhone/iPod touch/iPad. This is a serious problem that Apple need to fix internally; however, here are a few suggested fixes that may remedy your specific problem.
Make sure you are running the latest version of iOS (5.0.1).
Step 1) Hook up your iPhone/iPod Touch/iPad to your computer.
Step 2) Open iTunes (if it is not already open) and go to the music tab.
Step 3) Uncheck "Sync Music." This will effectively remove all music from your iPhone in an attempt to fix the Music App issues.
Step 4) After iTunes removes all of your music, unplug and replug your iPhone into the computer and go back to the Music tab.
Step 5) Recheck "Sync Music" and apply the changes to fix your Music App.
For slow Music App response on iOS 5, try resetting your iPhone, iPod Touch, or iPad. To do this, simply press and hold both the sleep button (at the top) and the Home button (the circular button at the bottom). Holding them for about 8-10 seconds will reset the iDevice and you should see the Apple logo. This will resolve many issues with the Music App.
Here is another observation made by many people on the Apple Discussion boards: larger cover art (approximately 3000x3000px) will also cause the music app to hang and often freeze.
If there are particular songs that are causing problems for the iOS Music app, simply converting them in iTunes usually fixes the problem. To do this, select the song in iTunes, right click on it and select "Create MP3 Version" or "Create AAC Version" (depending on your settings).
Some people are complaining about sorting in the new iOS 5 music app, this can be fixed by editing your tags in iTunes. Editing the fields "Sort Artists" and "Sort Album" will often fix sorting problems.
As a last resort, you can restore your iPhone either from a backup, or simply to factory settings. This will for sure fix your problem but you will have to resync everything to your iPhone. Very annoying.
In conclusion, it seems that the iPhone Music app in iOS 5 is very buggy and unstable.