The ladders have a couple of weak areas.
The plastic end caps that hold each rung in place can crack. The single screw on the end bends, putting stress on the plastic. If you want to keep them from breaking, you can clamp rubber gasket material around the vertical shafts to support the rungs.
The standoffs aren't strong enough to support the flex that occurs at the top of the ladder. The flex from using the ladder causes an up and down movement of the standoffs which eventually loosens the mounting screws. To prevent the up and down motion, you need to support the ladder from underneath. I recently ran into an adjustable door stop that's very similar to PVC supports that I've been using for a few years.
Here's a link. Put it under the lowest standoff and the flex will stop. I use 2 supports, but I suspect 1 would do the job.