I was wondering the same thing... perhaps the master link rivets were pressed too tightly. I'd image this could cause the adjacent link to pinch the roller and the increased friction cause it to fatigue. And yeah, new chain & sprox on the way.Apparently, the roller has had a fatigue failure.
I wonder if it being adjacent to the master link has had any impact on why this happened.
Because the load is being spread over many teeth, even if that roller fails completely, you should make it home.
Replacement is best.