The dust looks to be coming from the cover dragging on the gantry as it traverses. I didnt notice this when i started prints, and i didnt even have the print fail. It finished a 10hr print like this. It even autoleveled fine. But, i was not to pleased with the roughness of the print, which could explain why. So i wonder if these screws backed out durint printing, but if it did, the nozzle wpuld have dropped like 3-5mm. I think that would have made a big issue in the print. But, i didnt hear the cover rubbing either so i dont know.

As long as you saybthe screws are correct i will attempt to rejnstall the head and gobthrough full level again.