I agree that the threads can be making a difference. The thing about pre-tension or post tension though is that if the main tensioner is not touched but the pre-tension is - i.e. wrapping twice around something - something I see some LA'ers do, changing the thread path to make the thread change directions like Tate's doing, etc - the overall tension
has changed. Like you said, an increase or decrease in pretension will affect how the main tensioner has to be set. If it's not set differently, then the overall is an gain or loss of tension.
I'm more referring to the changes that are made in an effort to re-mediate the problem. The sudden changes are something that may be absorbed by the pre or post tension and hence why the problem seems to go away. If it's a twist doing it, perhaps that extra pre-tension is enough to sort it before it gets to somewhere it can snag. The extra twist that's introduced when running stack wound with the thread coming off the top is significant within a few minutes (like taking toilet paper off the roll from the top rather than the side). Cross wound can similarly have a problem when the spool rotates with it. It -expects- that extra twist action and absent that, perhaps can cause a similar symptom. I see that twist from cross-wound rayon thread with the embroidery machine. When the twists get numerous enough, all h*ll breaks loose.
If the problem was reproducible enough, it would be worth having someone sitting with the person sewing to watch the rest of the machine but that doesn't sound like an option here.
