So, if I read you correctly, you're saying that these types of cameras are just finicky when it comes to the way they focus. Right?
I can see where that can happen. With a larger format, a longer lens and a wider film plane depth of field/zone of focus can be a lot shallower, making focusing more critical. Since I grew up on 35mm SLRs with TTL focusing, I probably need to reprogram my brain to shoot with a rangefinder system. I'll just have to be more conscious about my focusing and pay attention to the scales more often. (i.e. If what I read on the focus/DOF scales doesn't jive with what my brain tells me should be in focus, I probably need to have the rangefinder adjusted.)
I will also consider using slower shutter speeds to test your theory about vibrations caused by the shutter springs. I have been trying to stay at 1/125 or above because common sense tells us that we should use a shutter speed that is greater than the reciprocal of the focal length when we hand-hold the camera. I can try 1/60 on a tripod. I can also try steadying the lens with the hand to dampen vibrations.
Maybe I just need more time to grok this rangefinder thing.