Q: my iphone keeps turning off mobile data for snapchat

Hi there kurt.extendo,

Welcome to Apple Support Communities.

If I understand correctly, the Cellular data settings for Snapchat are changing intermittently on your iPhone. If you haven't already, try the general app troubleshooting tips in the article below.

If an app you installed unexpectedly quits, stops responding, or won’t open - Apple Support

Restart the app

Close the app and open it again.

 

Restart your device

Turn your device off and back on.

 

Check for iOS and app updates

1. Make sure that you're using latest version of iOS.
2. Open the App Store and tap Updates.
3. If updates are available, tap Update All.
4. If asked, enter your Apple ID password. 

If the issue persists, try restoring your iPhone as shown here:

Restore your device from an iCloud or iTunes backup - Apple Support

Ciao.