How they handled it and went about it was wrong. Actual experienced practicioners may face those problems (see dukkha nanas / the dark night of the soul), but with proper instructors there are well-known ways of dealing with it.
> The article mentions whom ... the great and the good that attend and throw conferences, those that throw workshops and run retreats
What I was getting at is that <what> is ambiguous. "Mindfulness" is anywhere from jhana, "intensive meditation", etc, to more elements of stoicism. Practicing stoicism has just about nothing that can actively harm anyone or is dangerous. As pointed out in this article's discussion, the author has been conflating terminology which demonstrates a lack of understanding.
> Do you have evidence that the author was not learning from experienced practitioners?
Firstly, problems like the ones described in the article are well-known. Knowledgeable instructors are upfront about them and provide frameworks and guidance for dealing with them, instead of, as per the article, just "suggesting various ways that I might alter my meditation practice to alleviate my symptoms".
This looks to me like a case of the blind leading the blind in a consumerized and repackaged version of meditation that advertises "mindfulness/meditation" as a cure-all for one's problems. There is a reason that Transmission [0] is a thing. Just like even if I practice guitar for 10 years, that doesn't mean I'm actually qualified to teach it or provide useful guidance.