I have used Samsung music ever since the S5. Switched my audio using SmartSwitch from my S9. Had the "failed to play track" error. For the songs that have that error, I looked at the track details by clicking the 3 dots on the right side of the track. Noticed that the format wasn't an MP3 or M4A. I used an app called Audio Converter in the app store. Converted the songs that do not have the MP3 or M4A format. Now they work in Samsung Music app. Crappy part is now you have doubles in the music app. So you will have to scrub through those files and delete the wrong formatted audios. Hope this helps!