When I click a video thumbnail, goes to blank screen, progress bar and red flashing circle



Plex Pass / Apple TV 4/ Windows 10 Creator

On AppleTV , when I click an MP4 music video thumbnail, the screen changes to a blank screen except for a progress bar, then a small red circle flashes between 1 and 5 times underneath the bar and reverts back to thumbnail screen?

On Plex web using Firefox, thumbnails bear the label “Unavailable”

The same videos play fine using VLC on my PC. I must have created the problem but after a considerable amount of troubleshooting, I haven’t a clue. Maybe someone can point me in a problem solving direction. Help Appreciated, IM


_UPDATE: b _
Well, I resolved the problem myself by deleting the 'Music' folder from the Library and re-adding it. However, no idea why the problem existed - Best, IM