I checked the backside of the embroidery and noticed that the bobbin thread was too tight. I was using the bobbin holder with the yellow spot for embroidery. Didn't want to adjust it so found a spare bobbin holder and did a test sew with a small design and adjusted the screw until the bobbin thread looked okay.
I am using bobbin thread especially for embroidery and using the spare bobbin holder embroided the Noriko design without the previous problem. I am totally surprised that the embroidery bobbin holder with the yellow spot was so tight.
Kris in Aus
Trying to keep his answer tight, Jim says:
The yellow dot bobbin holder was included for use with very fine bobbin thread, which is commonly used in commercial embroidery. A lot of home embroiderers buy large cones of this type because it is so economical. With the regular bobbin case the very fine bobbin thread would often pull up and show on top, hence the yellow dot case. The bobbin thread you are using does not have this problem, so you will have no need to change cases in the future.