by From one day to another this mini circuit breaker stopped working, I had been using it wrongly as a on/off switch and was wondering if there was a mechanism inside to disable it after too many on/off switches, as MCBs are only rated for a finite number of operations.
Its really a mistery I suggest to compare with a new one to see whats different.
Suggested by commenters on youtube, it could be a missing wear-resistant contact point that was spot-welded to the arm, that has failed and fallen off.