This question here is asking whether there exists an example of researcher meeting particular criteria, in particular having solved a relevant open problem in the last 30 years and having initally been mistaken for a crank. There are lots of answers obviously not meeting the criteria (eg Galois definitely lived more than 30 years ago).
While I'd consider the 30 years to be a bit restrictive (50 years would be better, imho), overall the strict criteria seem essentially to make this question meaningful. As such, can we do something about all those answers not meeting them? A moderator deleting them all might be the most expedient way of handling this, but would also be somewhat heavy-handed.