I asked them if this happens a lot and they said "this issue sometimes happens" and they didn't tell me why this happens. Only to say "make sure that your torque wrench is calibrated correctly".
I thought it might have been from a hard shift in the trailer and the truck. When I was removing it I got the bolt halfway out of the post and then it stopped moving. Of course I had a torque wrench that was set at 100 lbs and it didn't stop me from breaking the bolt. I think that last time I put it on I torqued it down a little to much on the bolt, and definitely not 40 lbs of torque (over that).