I have had the DIamond since it came out! I love it and had to get used to a few things....but it runs like a champ.
So, as you rethread after a color change, that is where the problem comes in: try holding the top thread loosely as you push start (the foot goes down automatically on this machine) and let the trimmer do it's work. If you do not have the trimmer turned on, then hold the thread for the few stitches it makes until it stops to be trimmed. This little tweak can save hours of rethreading! Also check for bits of dust/fluff under the bobbin carrier (the black part)..lift out the bobbin, remove the plate, the small plastic that holds the bobbin carrier and the bobbin carrier. Use a soft makeup brush or a q-tip and slowly turn the hand wheel to get all the little bits and pieces. Surprising how a tiny fluff can cause all that havoc! Get it the dealer when you can, but usually it's just operator error, lol.