My music doesn't appear in Cs at all!
Beginning in iOS 10, apps now need permission to access the user Media Library. Sometimes this access can be prevented through Restrictions:
iOS 12 and later: iOS Settings > Screen Time > Content & Privacy Restrictions > Media & Apple Music
iOS 11 and earlier: iOS Settings > Privacy > Media & Apple Music
You may need to launch Cs to trigger the prompt for permission.
Songs aren't playing... or Cs seems slow and/or crashes a lot...
This could be a couple things. First, have you deleted Music.app? Unfortunately, at the moment certain Apple Music/iTunes Match functions are dependent on the stock music app. It needs to be installed for Cs to operate correctly.
Sometimes the iTunes Library can corrupt (usually following an iOS update). If this is the case you should experience similar behaviour with the stock app. Usually, a fresh sync of your music will fix the problem.
The music doesn't stop playing when I quit Cs!
Nope, it doesn't, and that's a good thing! Cs actually uses iOS to manage playback, to make sure that even if Cs is suspended in the background the tunes keep playing. Unfortunately, there is no consistently reliable way to ensure that a block of code is called whenever an app is terminated, so there's no way to guarantee that playback would always be stopped when quitting Cs. Instead I've opted for the consistently reliable behaviour, which is to allow playback to continue.
Cs is crashing!
If you are experiencing repeated crashes, sometimes a fresh reinstall will resolve things. Is Cs crashing under a specific and repeatable set of conditions? Congratulations, you found a bug! Please drop me a line and I'll correct it as soon as possible.
The troubleshooting page doesn't have my problem on it!
It's always a good idea to try reinstalling Cs first. If a clean install didn't solve the problem it could be a issue or corruption of the iTunes library database itself. Resyncing or replacing the music on your device may help.