When you say you changed the needle, did you go to a larger needle?
50 wt would likely work okay with an 80/12 needle, but 40 wt should be a 90/14 or larger.
And not just to a larger needle ... also what type of a needle are you using for FMQ on DSM?
Even for straight line quilting, I switch needle types.
My go-to is an embroidery needle ... but not my one and only for machine quilting.