Have you checked the screw that holds down the buckle to the toe strap? It could be loose. Also, you might want to put a tiny dab of BLUE loctite on it.
I have the Cartels and I noticed the screws were a tad loose but I didn't have the problem of wiggling buckles.
Every now and then I did notice that the toe strap would shift on my boot when I land bigger jumps. But this only happens on my rear foot and after several hours of riding. I think it's because of the snow getting inside the mechanism or freezing over the course of the day.