I would try everything recommended.
I have to say that I had a similar problem with my machine many years ago. Worked fine with the metallic, then suddenly started shredding. I had not even changed the project I was working on. I tried absolutely everything and nothing worked, so I tucked the project away in the UFO tote. I'd try again every once in awhile, but no go. After literally YEARS, that same thread on that same project worked fine. I think that there must have been some tiny piece of thread caught somewhere in the upper or lower tension mechanisms that I couldn't see and that I was unable to dislodge with my cleanings. My theory is that years of use finally dislodged whatever tiny piece of lint or thread was causing the problem.
Haven't read all the other posts, but I would recommend flossing between the upper tension discs (if you can reach them on your machine) and also using a magnifying glass to *closely* examine all areas of the lower tension mechanism. (If flossing, either use several strands of regular thread or ***unwaxed*** dental floss; waxed floss can mess up your upper tension discs.)
And, all I can say is, I hope you have better luck than I did!