I have a 2170 and a 2048 updated to a 2054. My machines work differently from one another. I use the 2170 for embroidery and rarely "sew" on it - it had the needle down feature but it does not pop back up when the pedal is tapped (maybe it should but as I dont use it sew it does not bother me). My 2058 has a "needle down" button in the front. When activated. every time I stop the needle stays in the down position (great for removing pins and pivoting). When stopped and at the end of my seam, I tap the foot pedal quickly and the needle comes up. Next time I sew it will stay down until the foot pedal is tapped or the button is pushed again.
As far as your bobbin issue - take off your throat plate, remove the bobbin case and either vac the bobbin area well or use a soft brush to remove the lint. Rethread the bobbin, change the needle and rethread that and then try again. Mine gets picky when there is lint in the bobbin assembly area or when I have "exceeded" (lol) the usefulness of the needle. We all do that - but I am getting better on changing the needle.
Good luck.