Loops on satin stitches

Hi,
We have trouble with loops when embroidering satin stitches on thin fabric, using polyester thread. We have tried to solve this problem, and technicians have tried, but no good result. It is on a SWF 4-head machine. On our SWF 2-head the problem is even worser. Has anyone experienced the same problem?

Location: 
United States

It could be a number of things from tensions to bad thread to scratches on needle plate.

Most likely because it all seems to happen on one side of the satin stitch, its either timing is off slightly on hook (see topic about off center bobbin stitches)

Or you have a scratch on the needle plate that is preventing the thread from being fully retracted by the take up lever.