I have the same problem with my Surface pro 7. Sometimes, the luminosity of the screen changes. But the fonction to adjust the luminosity according to the light around is DISABLED. It gets less brighter and more brighter without any intervention on my part. And I had that black screen twice.
I tried the Surface Diagnostic tool kit and it says that everything is OK.
I changed the color profile to RGB instead of "Improved" but I have the same result.
Yesterday I wanted to put on the night lighting and it didn't work. I tried to modify the luminosity and the Surface didn't react. I had to restart It to regain the control of the screen luminosity.
I think that there is a problem with the screen driver. But it is brand new. There is no update available.
I would like to have some help from Microsoft. Maby EdgarJr_A could transfer this problem to some specialists.
The problem is not always present. Sometimes it works properly. Sometimes not. I Think that the problem is more there when I am on the battery.