Spring problem - feather or main - feather too strong & improperly timed --- or main much too weak
Frizzen too soft with flint digging in and stopping. If this is the case, it is unlikely to be producing any sparks - at least, no white hot ones
We have not seen a picture of the cock at full throw, just with the flint resting on or dug into the frizzen's face (which is unlikely to be full throw).
Cock at full throw should have the flint, even a short one, closer to the pan so that it has scraped the frizzen full length. It is
obvious the flint is in the shady area of too short, but the cock's top jaw has not hit the frizzen, thus the lock should have worked.
If the flint is too short to work at all, the top jaw - or screw would have struck the frizzen's face.
If this last picture is the cock at full through, the lock needs a new, properly made tumbler.
In that lock, my opinion is the flint is too short to be shot bevel up causing it to strike the frizzen too far down it's face. In this lock, the flint should have been mounted bevel down, so it scrapes more of the frizzen's face.
Lets see a picture of the cock at full throw.
A rebounding frizzen should be striking the flint just back from the top front edge. The fix for that is different timing on the
frizzen's throw and rebound, along with possibly a stiffer feather spring.