I know it sounds simple, but it's often overlooked. Could you try restarting your device? If that doesn't help, try a quick clean reinstall of the app. Just followthese steps.
If you're still having trouble, could you let me know the exact version of Spotify and the exact version of the operating system you're running? I'd appreciate any screenshots of how your app responds to your commands to play your local files as well.
I'll see what I can suggest next!
Help others find this answer and click "Accept as Solution".
If you appreciate my answer, maybe give me a Like.