The Star Trek: Voyager episode "Threshold" is a popular target of ridicule. Its treatment of the warp scale appears to be inconsistent with the rest of the franchise, and its treatment of evolution is also inconsistent with science and common sense.
What? JANEWAY is evolving! JANEWAY evolved into... ???!
I've seen many quotes from cast and crew expressing regret about that episode. However, I've also seen a more extreme claim frequently repeated online: that the episode was considered so bad, and so nonsensical, that the writers later struck it from canon altogether -- the only time that this has ever happened to a Star Trek episode.
Is there any evidence to support this claim? This could include comments from the crew, or evidence from later episodes. Also, if true, is this the only Star Trek episode that has been treated like this, or does anybody know of other episodes also be retconned out of existence?