That is not 'play' in the hub, that is gear lash in the trans. Pertectly normal
Take another look at the video. If it had anything to do with the tranny, the nut and shaft would me moving as well. I assure you, the shaft is not moving when I am rocking it back and forth.
I pulled it out of the bike and confirmed that the steel insert is loose in there. I could probably pull it completely if I tried.
I have never seen this happen before and I'm curious if Yamaha
would warranty the part or not. If that boss let go on the face of a large jump, I am pretty sure it could end pretty bad.