This sounds like a fat rendering issue.
Temp not high enough and/or long enough to properly render the fat well.
And, or, in combination......
You bought a bunch of chicken wings....if the wings are from old birds — that can certainly contribute...they don't give up their fat as readily as young birds.
Older birds also tend to have more flavor, which may also explain your comment ....."I have never ever tasted stock that was so utterly perfect,"