Hmmm, I’m not sure. I was flying flat-and-level towards the destination, so I suppose the Collective was about 75% or so, not max. After I stopped my forward motion, then the helo started to drop, and I pulled up on the Collective (to maximum) but nothing would stop the downward fall.
Also, it only happened in that helo Certification mission/exam. Later Career missions with the G2 did not have the problem.
It is not impacting my play: I got the Certificate on my fifth try, and I moved past it. My primary goal in reporting the bug is to notify the developers and other users.