The following are active issues for Halo: Reach as of 10/13/2021 in build 1.2580.0.0.

User Interface (UI) 

• Any camera turning caused by a view angle restriction while in a vehicle passenger seat will stutter above 60 FPS.
• Players are unable to enter the gameplay after setting language to Portuguese, Japanese, Chinese, or Korean.
• For Steam, please see troubleshooting steps (Full article).

Gameplay

• Moving from an enclosed area to face an open area in any map or Campaign mission causes a significant drop in performance. This is most common for PC players with unlimited framerates.
• Player models appear to briefly desync when moving after an assassination.
• When entering an elevator in co-op or Multiplayer, players will briefly appear to play a falling animation.

Campaign

• Mission progress resets to the beginning of the mission when selecting Resume Campaign after switching between an Xbox One console and an Xbox Series X|S console.
• Cutscenes during "Tip of the Spear" can see performance drops using AMD graphics cards.