Why does the screen turn off whenever I scroll down on the touchpad?

Had the same thing happening, though only in the browser while doing two-finger scrolling with the touchpad. If used touchpad for other things (like click), or scrolled in some other app (like PDF reader), things were fine. Later found that using Wacom tablet was also causing the same issue. Found via a Wacom reddit post that resetting display card driver does the trick. Worked in my case. First tried to update Intel HD Graphics driver, but had some version incompatibility. So in Device Manager, went to Display Adapters, did "Disable device" for Intel HD Graphics (causes screen to flash etc, as it reverts to Microsoft's own basic driver). Restarted system, re-enabled driver (if you continue with the basic driver, games etc may not work), now things are fine.