Dima had every right to a let as well if you actually watched the video. Let's not make this about what the umpire called or did not call. Lin clearly called it, and if he had missed, it would have been a replayed point.
the point was actually complete
there was no let call before that final edge, because everything was so fast.
I think Lin at first didn't see the edge, because of the light
Dima said it touched
the umpires awarded the point to Lin and finished
and then override to replay point
So it is fair to say Lin was robbed by the lighting staff. Without that light, the point won't be replayed and if the luck remained the same, the same edge would still happen.
only debatable part is, if the light caused the edge. Maybe, maybe not