I have been using the X-56 for a couple of years now, have had MANY problems, but not that particular one. I "fly" FSX SE and Elite Dangerous Horizons, and have experienced a succession of problems but never a "snapping out of control" while inverted.
i'm no expert, but that sounds like a PC problem with the program rather than a problem with the controllers themselves.
If BOTH X-56 controllers are doing the same thing it's a program issue. If one were doing it and the other not, I wouldn't be surprised. But Both??? Nah, it's program.