I am quite certain it isn't the fabric causing the problem....I have sewn with this weight of fabric frequently and no issues. I did a bit of playing around and under closer examination while sewing, I can actually see the entire needle/shank assembly jump to the right. It is almost as if something isn't quite tight enough in there. Headed to the sewing machine repairman with a sample this morning to see if he can help me without a service call right now.