Which is all a pretty silly discussion because this is an important concept in the law where it has been discussed and defined rather well in a clear process already. Being interested in the question is not an issue, having a declared interest in a specific outcome is. It's still not an easy problem but here it's like the entire discussion is happening in a vacuum.
On this it goes beyond direct financial interest. Several PACE researchers have been advising those treatments for decades, they built their reputation as "top researchers", nevermind how cringeworthy that is, entirely on those treatments. Even without the specific conflicts of interest of being paid advisers to medical insurers, they had a very strong incentive in proving themselves right, as admitting the uselessness of their treatments, which they found in PACE as in every prior trial, would have essentially ruined their career, made it clear they had given bad medical advice, in a paid capacity, for years. They had interest in the questions being asked, no issue here, but more importantly were deeply vested in a particular outcome that would have affected them personally. It's scandalous that they were even allowed to grade their own work, having decided on the test questions themselves in the first place. To further having taken part in the Cochrane review is just a complete breakdown of the entire process.
It's just weird that there should be so much discussion over something another field has largely settled already. Conflicts of interest are generic, not even particular to research or medicine. Recusal is not a penalty and it's not as if there aren't enough people out there with sufficient skills and no stake in any outcome. The 66% rule is particularly absurd.