I just got a chance to watch (missed it yesterday and been really busy so didn't have a chance to get to it until now). I noticed at ~21:01 to 21:04/21:05 in the video, something whizzes past the F9 core while it's on its way back to land. Anyone know what that was? Here's a link to the video at around that time:
It looks dark when against the blue of the planet, but almost grey when it gets into the darkness of space. Chunk of ice? Meteorite? Satellite? It moves past really quickly and doesn't really appear to come from the stage, but below it.