No failure was identified
"even as it admits that it still doesn’t know what caused the life support systems to malfunction."
A more correct statement would probably be "because it doesn't believe the life support systems malfunctioned.", although they'd never come out and say that.
As you say in the article there is no evidence of any malfunction other than the pilot's report of symptoms. While that can't be ignored, there are other possible causes of those symptoms and part of the action the USAF is taking is additional training directed at avoiding those other causes.