I would:
1: Change the needle, its a cheap alternative to being frustrated.
2: Check to see if the quilt is loaded too taught or too loose.
3: Try another design and see if that design stitches ok, I have had issues with some designs in the past.
4: Try another thread to see if it indeed the thread.
5: Turn off and to a complete reboot of your longarm.
6: Delete and reprogram your design.
7: Is your backing regular quilting cotton? I have seen issues where someone used a high thread count sheet and had issues with quilting it.
I am sure others will be along with more ideas, it can be frustrating at times.