Sometimes screen remains black after boot sequence (A04 standard OS image)

Fortunately, that is normal for USB devices. (Maybe not normal per se but it’s not a problem. It happens on busy machines.)

X Server is falling back to an older method for detecting framebuffer devices

Oh, that’s not a problem, either.

This looks like all Xorg logs and it looks fine. It looks like it detects the display and even gets the EDID, so maybe it’s just that the backlight wouldn’t come on. If you try to ssh in and turn the backlight on from the shell, that might work.