If you do not have a better method, I have one that may help you. You can choose to convert Spotify songs to MP3(I use Tunelf Spotibeat Music Converter) so that you can use other apps to play them.

I guess this is the problem of iOS.
Have you tried to update the iOS and the app? May be these will help:
1.Update the iOS and the app to the latest version
2. Force Restart iPhone to Fix iPhone
3. Use iOS System Recovery to [fix iOS system free for mac](link url=“https://www.tuneskit.com/ios-system-recovery-for-mac.html”)
4. Using iTunes to Fix