Because you are moving side to side, the needle flexes side to side and may affect your timing just enough to throw off your stitches. A stiffer needle, perhaps larger or a different type, might help.
Don’t know if this would work or is possible on your machine but on the sweet sixteen they suggest turning the eye of the needle just slightly towards the five-thirty position instead of the six o’clock position if you are having thread shredding which is also a timing issue. Maybe something similar would help you.
Next time you take it in for servicing ask them to check the timing and set it correctly if it is off even a little. That may help.