The only failures I’ve had in an S&W revolver were unburnt powder under the extractor star causing it to lock up (Unique powder) and a pre-1961 ejector rod backing out and locking things up. In 1961 they changed them to a left hand thread to prevent that.
I’ve had the ejector rod problem too.I wrapped a piece of rawhide around the rod and tightened it with pliers.