When I thread paint, if having trouble with the metalic thread I try these things first. (larger eyed or a metalic needle,change in tension, slower even speed) If still won't work I tape a safety pin upright onto the right side of machine, place the thread in a glass or pint jar etc, and then thread the metalic thread through the safety pin and rest of machine as usual. Not sure why it works, maybe takes some of the twist out before it gets to the needle? Good luck.
Laurie