In contemporary parlance, “problematic” connotes to me that said individual expresses ideas, in their words, speech, or way of life, that are anathema to the dominant paradigm of thought/manners/civility, but does not necessarily imply anything about the mental health of the related individual.
Disordered thinking of the quality you’ve described is indicative of a serious psychological unwellness that, as the other commenter suggested, suggests paranoid schizophrenia or a related form of psychosis. But I don’t intend to seriously engage in back-of-envelope psychologizing.
Prattling on about irrelevant history and insinuating 9/11 conspiracy theories in a courtroom not at all concerned with either of those items does harm credibility, and I think rightfully.
For reasons of both family and personal history I am genuinely sensitive to the phenomenon of the “deemed crazy” person being consigned to permanent non-consideration of their words and expressions, their concerns, but I also recognize that such legitimate unwellness poses genuine issues for the believability of anything they claim.
Putting my extended aside aside, I would phrase it as “how many people are telling the truth about something, but aren't taken seriously because they're severely psychologically disregulated generally.”
It’s not necessarily outrageous for me to assert that I warned the FBI about 9/11 in June 2000. It seriously harms my credibility if I decide to bring up this grievance when I’m speaking to a judge about my undeserved traffic ticket in October 2024.