Have you tried quilting on another test sandwich? I recently had the worst time with shredding and breaking on a certain material. I still don't know why it was such a problem, but I won't use that material as backing again.
I hope you find the answer soon. I know how frustrating this can be. I'm so sorry for your loss. It is great that you turned to quilting to help get you through the grieving process and to this board for assistance.
I'm sending positive energy to your machine to knock off the hassling.