I just made my first score on Musescore 4 and placed the first notes in Percussion 1, snare. I clicked the "return to start" button then I clicked the "play" button. The blue line that moves during playback showed up right before the first measure and didn't move. There was also no sound and nothing I did could make the program play. I also realized that there wasn't any sound when I put the snare notes down onto the staff. There was always a similar issue in Musescore 3, but it would usually fix itself in a minute or so. This is not the case right now, and I'm certain that it's a Muse Sounds issue.