Reason behind Pixel 4's 90Hz mode issues discovered in code commit comments

Pixel 4's 90Hz screen drops back to 60Hz when its brightness drops below 75%. Google promised to fix it, but hasn't offered an explanation why this was necessary in the first place. The code commit comments might have managed to fill us in though. It seems that the display uses different calibration profiles for 60Hz and 90Hz modes. And the display maker hasn't matched them perfectly, which leads to slightly different brightness levels. Slight, but still enough for people to notice it when the screen goes from 90Hz to 60Hz or vice versa (and it does switch fairly often, e.g. there's no...