I have a Garmin Forerunner 955. I loaded a bunch of music onto it and was able to listen to it without issue. UNTIL I added Spotify. Now my "Music Controls" control on the watch doesn't let me control the mp3 files I loaded onto the watch, it just lets me control Spotify.
But I cancelled my Spotify Premium and Uninstalled Spotify. However, that Spotify control is still on the watch! And when I click it, my watch just crashes and restarts. So I'm not sure how to get to my music. I hope the answer isn't going to be to do a factory reset.