Seems like you are putting this LCD on the Autoclave machine for a very long time to remove small bubbles. At least that happens to us when when put for a very long time. A simple backlight replacement will do.
OFF THIS TOPIC. Been doing great on screen refurbishing but seems like on the iPhone 6S once i place on "KO" lamination machine - the screen has lots of Big bubbles. I have done thousand of iphone 6 & 6 Plus but i can't get it right on the 6S. Any suggestions on this? Thank you