pretty sure its just a random occurance have many bushels are you holding and rough terrain? i could really only see speed/terrain/weight as your factors I think most people are just going to the the big singles.
There was a campaign a few years ago to replace all that hardware. If yours qualified, and you didn't get it done, that's the first step. I have 420+ bushel in my tank. Did lose 1 bolt this year. Know a guy that was having trouble with a 9070. They took all his bolts out, just left the studs, and he hasn't had a problem for 2 years.