I've never experienced it and I use the original threading on all of the Slants I've used but I'm about to have another 411G show up and it's not been maintained at all in recent years. I'll compare the two that will be here and run the bejeebers (<- weird! Firefox doesn't think that's a word...
) out of the "new" one and see if I can make it misbehave then try the alternate threading and then your alternate alternate.
How intermittent are we talking? Every couple of days... I'm going to make a lifetime of quilts before I see it...
Maybe in terms of hours of use is better - for me a couple of days of sewing is probably a couple of hours,...