Loops appear during sewing.

If the loops are formed on the reverse side of the fabric, increase the upper thread tension by selecting a higher number.

Please also check whether there are any loose threads or fluff in the tension discs. If necessary, clean the space with a toothpick or a brush.

However, if the loops form on the surface of the fabric, reduce the upper thread tension by selecting a lower number.

Please also check whether there are any loose threads or fluff beneath the plate spring.