SOME sheets work just fine. Others cause major problems. I have one on the machine right now, and I'm at a loss what to do.
It's an old (previously) hand quilted quilt. Some of the threads have worn away, and she just wanted me to put machine quilting in the missing areas. This quilt has been wash numerous times. It's been well used - some of the embroidery has been worn away, too. It has a very thin cheap batting.
It was one of her first quilts, and she's been doing this a long time now.
I've used every white thread in the place, top and bottom. I've adjusted tension, speed. I've even said bad words (then promptly apologized - my studio is in a former church). I use a practice piece on the side and get beautiful stitches, with every combination of threads. Move to the quilt and get cr@p!! Huge skips.
If it weren't for previous bad results with sheets, I wouldn't know the problem. For the charity quilts, all of us who use the longarm to quilt them have said no more sheets, unless they are flannel. It's not worth the hassle.