(Want to preface this by saying that I 100% think it was in.)
While I don't think it was bouncing, watching the replay a ton it looks like it could be riding up Andersen's pad.
If it were flat on the ice by the point it was 'in' the net, then how come we can see Andersen's pad beneath the puck in this shot?
If it were flat on the ice, pretty sure that'd be physically impossible.
Still, based on how little it comes up off the ice, with how far back of the goal line Andersen's foot still is, and with how much white of the ice we can see between the goal line and the puck, not sure how that wouldn't be in.