This is a common misconception about the review. It is true that none of the studies they looked at were double-blinded but they were still included if they were designed and conducted well enough. In a Q&A shortly after the review's release Cass demonstrates that she is well aware that exclusion based on this would be silly.

https://thekitetrust.org.uk/our-statement-in-response-to-the...

The amount of myths circulating about the review prompted the publishing of an FAQ page which deals with some of the more egregious examples (e.g. the claim that 98% of studies were rejected).

https://cass.independent-review.uk/home/publications/final-r...

I think it's naive to call a series of "myths" coming from the same camp as misconceptions.

There was a (successful) effort to push misinformation regarding the report.