Same for me I got my 820 in 2010 and since I had a lot of troubles with the BSR. After 3 or 4 minutes of free motion I have a lot of large points. My friend has exactly the same 820 and she has the same problem. Also, sometimes the sewing machine just stops sewing. So, we make our quilting on the 440. I even get better quilting with my old 1008.
It's really a pain.