Good quality picture David. To me it appears that you are picking up lint from another source. You say that the mass is a lint ball, that the thread itself is not frayed. Appears that there is a bit in the thread guide too. Analyze the shaft and look for lint collection there as well. I've found some of the fabrics I use, epically flannel, tend to kick up lint. Darn stuff gets up into the tension spring. At least you can catch the upper thread lint while you're sewing, and brush or pick it away. It's when the bobbin coughs up a chunk, which gets sewn into the stitching, that I dislike. Just keep the machine brush, old tooth brush and notebook handy and use frequently. Write down your observations, fabric you are using, thread weight, needle size and frequency with which you clean the apparatus. Soon you'll be teaching all of us.