In short, I don't know, but I will share what I do know from research and anecdotes from my experience.
If you don't know, Monat is a multi-level marketing company that has been receiving complaints of hair loss since 2015, and complaints between 2015 and 2018 were consolidated into a class action lawsuit. The suit settled without the Attorney General giving an opinion on whether Monat had done anything wrong, and Monat was not required to admit fault. They were only required to pay $250,000 in fees, with $82,782 going to customers.
As a veteran stylist, this was very reminiscent of the Wen Haircare lawsuit of 2016. This lawsuit had similar allegations but paid about 26 million in fines. Wen had a much larger parent company in Guthy-Renker and more complaints.
In both instances, no specific ties were found between hair loss and the products, but obviously many people had adverse reactions to the products, and I think I know why.
It isn't necessarily the products themselves but the products not being appropriate for every consumer. In the case of Monat specifically, it is sold by a lot of individual independent salespeople as part of the multi-level marketing business model. In this type of business model, it becomes more important to have other sales people signed up under you to bolster your commissions than it is to have general customers just purchasing product. In business models like this, they can grow fast in small areas, which can mean a lot of competition to sign people under you first. That competition and a lack of education during onboarding can often lead to independent salespeople making false claims about the products, which then leads to consumers purchasing product that may be inappropriate for their hair. Based on the lawsuit terms, it sounds like the independent salespeople may have been making false claims about the product, and there wasn't an adequate return policy for unsatisfied customers.
Now for my anecdotal information. During both the Wen craze and Monat craze, I had clients try the products. I had two clients who tried Wen and did not have adverse reactions. My client who tried Monat had an adverse reaction—the product caused a lot of breakage and thinning of the hair. When this client reached out to the person who sold the product, the person did not offer any solutions.
When all is said and done, I think anytime you plan to spend your money on a luxury product, that product should have a robust return policy and well-educated representatives that set you up for success in your product choices.