Did you ever check the slop in your hitch receiver. I know my Ex has a fair amount. If the hitch shank rotates in the receiver on a turn, it will add a rotational force on the unloaded (inside) cam which could force the cam outward making the frame bend as your picture shows. There is not a lot of space between the bar and lip of the cam to absorb that movement. Plus
I found that my bar wanted to rotate outward because of that binding action. I would try to post up a picture but I no longer use/have the Reese Dual Cam hitch.
I completely follow John's thinking, and logically one may assume bending and failure is caused by the heavier weights. I'm just adding another perspective. Also, keep in mind that this outward force from the inside bar could have enough force to pull the snap bracket outward bending it.