RE: Fire
It looks like the washer was between the copper pad, on the PCB, and the Eyelet connector on the cable, this is incorrect assembly
the screw and the washer are both stainless steel, which is a comparatively high resistance compared to the copper on the PCB and the tin plated coper of the connector, which, as you have found out, causes localised heating
give the surfaces of the PCB Pads and the connector a scrub with fine sandpaper or scotchbright pad, and re assemble correctly, hopefully it will be ok afterwards, then reprint the cable covers
regards Joan
https://help.prusa3d.com/guide/7-heatbed-psu-assembly-silver-psu_33512
I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility. Location Halifax UK
RE: Fire
Good advice. Thank you.