Unfortunately, some players have identified an issue that occurs due to variance in controller hardware, commonly referred to as slow turn bug. This can cause players to become unable to, or inconsistently reach what we call a pegged state.
The pegged state is a region in the outermost range of the analog aim stick in which we blend the players turn speed to a much faster rate. This issue is compounded as the control input fluctuates depending on multiple factors - if you are applying even the slightest bit of downward pressure (clenching), moving the stick around the edges a bit (which is why its even more problematic when aiming diagonally), or torqueing the stick on the edge a bit more than normal on some controllers.
The good news is we have a fix for this issue that introduces no perceivable change to the current feel of the game. This change is going through test and pro team validation now and we will have it out to you soon.
One thing that has become clear in absorbing all your feedback is that Halo players want choice when it comes to controls. And with that in mind, we are also working on another little pet project that will allow even more precise tuning. This update will offer more custom fine-tuned control over controller settings (hint: independent vertical/horizontal sensitivities, the ability to calibrate your own dead zones, more granularity in sensitivity, and more). We hope to have that out for you in December and we will follow up with more details later.