iPhone 6 - screen replacement - no auto-brightness - laggy screen

I replaced the screen on my iPhone 6 with the iFixit iPhone 6 LCD Screen and Digitizer Full Assembly. Since the replacement, my phone no longer auto-adjusts the screen brightness and the screen has become very laggy, sometimes causing the screen to freeze, sometimes opening things I didn't touch, and sometimes not recognizing my touch at all.

I took the phone back apart to make sure all connections were reseated properly, however the problem persists.

I tried to remove the front facing camera and ambient light sensor from my original screen in hopes of replacing that part of the replacement screen, but the ambient light sensor disconnected from its cable in the removal process, so that is a no go.

I never had either of these problems with the original screen. Is this happening because my replacement screen is faulty?