It looks like a Merlyn copy to me. I've never seen any enclosure fail in this way. The sheer weight of the glass on the runners has caused the break. Bad design
Dont think its been caused by weight as its not weight bearing its only there for the door to stop.
On closer inspection from what i can see, i think someone may have pushed tge stopper bracket in, because it isnt making good contact with the the runner which the stopper is on, and cracked it. Ive worked with cheap ones and expensive ones and one things for certian, tgey are all made out of cheap alloy which bends, buckles, scratches and brake way to easy.
No matter how expensive they are.
Kno by experience 🙁