Thank you @N6722C.
EDIT Ok I found what’s triggering the de-sync in such a short time. It’s pausing game. While paused, any drift in my controller is moving the cockpit heading indicator in that direction. I can sit here and watch it move a degree or so per second. When I un-pause, the aircraft is still pointing the way it always was, but the heading indicator has spun a value relative to the pause duration and stick drift.
Sure enough, hitting ‘d’ while unpaused reset the cockpit and HUD to match.
Thanks 