Why my LED screen seems not brightness?

Yesterday, our engineer help a customer , which have a LED screen very less of brightness.

After we get the photo of the screen , yes it’s really one.(As the Photo)

and our judgement is, the OE of the screen set wrong.

After fit it, the screen become much brightness now .

Usually the Brightness problem becouse us this list:

bad LED screen , Especially since the Bad LED CHIP
the OE sit wrong
The Power is not enough (Usually it’s seems red)
The screen is very old one, over the age of screen.
…… and more ?