So it sounds like there are a couple of different issues. But Brad Smiths above sounds most like mine. Both my iPhone XS Max's do it. Here's the scenario: When auto brightness is dimming the screen (say from 50% down to 10% or something), when it hits around ~20% there is a big jump down in brightness that appears like a flicker. Above that 20% mark it is a smooth transition, and from 20% down to 1% it is smooth too. You can test it by going to brightness screen, stand somewhere with bright light, then move somewhere with no light. Watch the slider go down and then watch the white area of the screen and you'll see it 'flicker' down in brightness. Both my phones do it. Anyone else experience this?
[doublepost=1538365442][/doublepost]Just realized that you don't need to use auto brightness to test. Just slide the brightness bar really slowly from about 5% to 30%. You will hit a point where brightness jumps dramatically instead of smoothly. It MAY be software because the point is not set, it actually seems to move a little bit. But somewhere around 18%.
Yes, I see this exact behaviour. Like a split-second drop in brightness around the 18% mark. Also happens (but to a far lesser degree) around the 45% mark.