I've had this happen as well - on an old 620 folder. I finally worked out it was one of the 620 spools, that had excessive wear on the winder hole. Lots of slippage when I wound on, so it didn't wind as tightly as it should have. Ended up with a "fat roll", but not quite that fat. ;) Worst thing is, it started winding perfectly when I loaded the film - only started slipping as I continued to shoot.
I did process it, after hurriedly putting it into a film pouch, and whilst it did have some awful fogging, quite a few frames did survive (thankfully!)
Once I laid the exposed film down before securing the adhesive ribbon, and cringed as I heard it unwind. That taught me a quick lesson, but fortunately the fog did not encroach on the images.