When you down shift to second its sounds like it going too far past second.
Try a little more investigating and see where neutral is after you down shift to second before you let the clutch out.
Neutral should be an easy touch on the shifter from second.
Also while you are coasting with the clutch in, go back and forth in the gears at low speed and get a feel for the way it shifts.
Check your clutch adjustment. Give the clutch lever a longer pull and see what that does.