
Cause: The PCB maker that Helder used didn't set up their machines correctly and the ribbon cable of the screen is not making full contact with the pads on the screen PCB. This is causing dark spots on the bottom of the screen and possibly even the screen not working at all.
Fix: It is actually pretty easy to fix this issue, All you need to do is very carefully separate the screen from the board while leaving the ribbon cable attached, and reflow the ribbon with flux. It would be easiest to get a flux pen if you do not have one already. Just add a little bit of flux and run your tip over each of the ribbon connections.

This may take a few tries to get working properly. If using just flux isn't working, try adding a little bit of new solder to the pins.
Helder made a video on his Instagram about the issue and how to fix it. It can be viewed here: https://www.instagram.com/p/Bu4pEUrF3C5/