I have the 430 which is essentially the same machine. When I'm chain piecing I have problems if I go more than 6 or 8 stitches between pieces. The needle will either pick up a loop of bobbin thread or the top thread will break. I usually don't go more than a 4 or 5 stitches without fabric so it doesn't happen very often.
What Bernina is telling you sounds wrong....at least to my ears. Hope you get this worked out. Would love to know the ultimate solution.