Troubleshooting steps for this common issue:
1. Ensure app is updated (seems obvious, but still good idea)
2. If you have any battery-saving or optimization apps, ensure there are exceptions created for Pandora to avoid troubles with that.
3. Sometimes it helps to clear data and/or uninstall/reinstall it. Nonetheless, at least be clearing the cache in the app every time after use.
4. Ensure background data is on and unrestricted.
5. Ensure any screen auto-lock settings are unchecked/turned off in Pandora app settings.
See how this works!