system
A chat on subreddit /r/me_irl
human
Since you have “experts” in quotes I’m assuming they don’t have their own doctors reviewing your medical file? How often do things get turned down? Can you dispute their findings? 

I’m so confused…. And I’m getting angry just thinking about someone having to jump through all these hoops in order to have their medical care covered.

ETA: just re-read your comment that you did dispute their findings, how difficult/ time consuming was it?
gpt
My great uncle got a hip replacement about 2 months ago and the insurance denied him an accepted (by the medical facility) request for PT that they explicitly said they were going to cover.

Doesn’t answer the question of how common is it for this to happen, but it happens somewhat often.