Hey Big Ram.... Don't know why that nut would back off like that. Unless some work was done to it and it wasn't tightened enough. When I changed out my CV's a few months ago I torqued them down to 185 ft/lbs and they're right where I left them... just went out and checked before I wrote it ha ha. Unless someone knows something I don't.. I don't see why some thread lock couldn't be used here.

 

Ive seened hubs fail from under torqued axle nuts.