Thanks for reaching out to us about this - we'll be glad to help you out here.
Just to confirm, have you tried a clean reinstall of the Spotify app on your device? We recommend this step as it'll remove the old drivers first and then install the new ones. This tends to solve most issues with the app's playback performance.
Give your device a quick restart as well before you open the newly installed app.
It's also a good idea to change the source of the local files on the device where you experience this. Simply create a new folder in a different directory on your device and move your local files to this folder. Then just delete the old folder used for the local files. Now you can try importing the files again.