Well, I can't see a chassis that's undergone even halfassed FEA collapsing under itself
If its fit and welded by a knob its not a stretch.
We had to re build most of our frame last year for this exact reason. The weld strength tests we are supposed to do to show that the car wasn't built by a moron showed just that.
Stuff gets broken a lot at baja competitions. Generally its a combination of a lack of mechanical sympathy from drivers, errors in building (something was measured wrong and welded in and not noticed), parts being underbuilt for the application, or trying something new that doesn't work out. In the case of the last thing, our full hydraulic steering setup (think replacing tie rods and steering rack with hydraulic cylinders), they were basically retrofitted in, rather than designed-into the front suspension, and there was a sideways component to the forces they saw, and we broke our cylinders.
I can imagine that aside from the jumping and crashing into stuff that we do at baja, all the other things apply, in addition to the can of worms that can come from people being allowed to screw with the engines.
Also, there may be some work done to stuff a bike motor into the old baja chassis for maximum death potential.