Auto-Brightness setting present but not working. Screen replaced

After replacing the display assembly on my iPhone 6S the auto brightness feature has stopped functioning. The replacement display was a complete OEM genuine assembly taken off of another iPhone so the sensors are genuine.

I still have the option to turn auto brightness on and off in settings (iOS 13.2.3) but the brightness doesn’t actually change depending on the light level in the room.

I have reset the phone in settings, should I try resetting it from iTunes instead?

Thank you,

Oliver