Fascinating pistol!
Regarding a weakness, yeah, it looks like the screws holding the frizzens broke off. There is a screw hole on both sides, just in front of the pan, and just above the spring. Both seem to have the remains of broken screws in them. On the right side it looks like the screw broke off just below the edge of the screw hole. On the left it looks like it broke off and left a stub sticking out of the hole. A larger (thicker) screw there might have helped with this, but the problem may have been with heat treating or case hardening. If the guy case hardened the screws, then they may have been brittle. Perhaps the position of the screw hole was also a factor?
Later locks have a design improvement, a "bridle" for the frizzen (sometimes called a "pan bridle"), that helps avoid this kind of break. (I realize that most of you reading this know this, including the OP, but I think it's helpful to explain this for new arrivals. I'm talking about a small extension off the side of the pan through which the frizzen screw can pass.) That improvement greatly reduced the amount of stress put on the frizzen screw.
Bridled frizzen

Unbridled frizzen
