There was, and still is, and Apple even acknowledges as much: "There is also a bug that is affecting some animations built using Core Animation that Apple says will be fixed in an upcoming software update."
Hard to say. The thread is from Sep 24; the Wayback Machine has it archived on Sep 25. So either it was already published and virtually no one knew about it, or it wasn't published.
The documentation is also a bit obtuse on what is and what isn't supported. The original question was whether UIView.animateWithDuration supports 120 Hz, and the docs don't really explicitly say one way or another.
There's also a
tweet from Sep 14 that links
another recent API, which is ostensibly for 120 Hz support but to this day isn't documented ("No overview available.").
So while I continue to think a mountain is made out of a molehill, and the people who think Apple tried to screw someone over or is trying to have the 120 Hz feature all to themselves are bonkers, I also think Apple hasn't so far done a great job documenting this.