Has anyone encountered this happening with videos on SL360 on AWS?

I've uploaded a SL project to AWS, made all files public, and the very first video embedded in a slide plays perfectly. But then the rest of the videos look like this and don't play. 

All the mp4 files are pretty much the same. 

I'm using the modern player, so the presentation is all HTML5. 

Don't understand why the first one plays, but not the rest. Any suggestions you might have would be greatly appreciated. 

I should also add that when I view them directly from AWS and the path listed, they play fine. So nothing is wrong with the videos per se, just once they are called up from SL in the player.