Hi
Iv had this happen to me with screens and it caught me by surprise!
It’s probably not a issue with the device it self as like you said the old screen didn’t have this issue
So here’s what I would check!
Check that the connector doesn’t have any black or burned pins on the connector as this can cause the issue
CAREFULLY check the ribbon cables for any debris or exposed copper or tears and this can cause no backlight
Finally I would try cleaning the connectors on both the screen and the device while it’s off with a high percentage of isopropyl alcohol as this can remove microscopic dirt that our human eyes can see!
If none of these work don’t loose hope and shoot us another message and we will try some other stuff!
Hopefully this helps though
Thanks:-)