Also check the tracking via Track IR Bubi, if it loses sight of the points of light, it gets flakey. I find if AH drops, I have to restart trackir also.
Would also check for any errant light sources behind you, as it gets a bit freaky at times when you get them.
Check also that your trackclip hasnt dropped down a tad (makes tracking the light points a pain if its not pointed at the camera)
Wurzel (Have a fantastic new year bud)