In my case it was a horizontal travel metal blind shutter on a Contax IIa.
The lower curtain was moving too slow.
I was just last night reading a leica pdf to try to get a grip on how that shutter works. They were talking about another issue described as shutter bounce from a weak braking system that if the OP's problem isn't the hinge may be a possibility.
What do you think?
It probably is the hinge in this case but it is useful to try to diagnose these problems and learn how to rule things out.