Ive noticed both on my 8k x and 5k + that at least for me it impossible to get it completely jitter free when using lighthouse. If its slight Base station vibration or something else i cant tell you for sure. The internal tracking is however rock solid and you could do it like this. If both show movement move, if only lighthouse show movement dont move. If lighthouse loose tracking go to internal. Something along these lines. As far as i know this is being combined in controllers so is it possible for you to do this? I dont know how much lag such a condition would introduce but i cant imagine it be much.
I suppose should note that since internal does not do 6dof it would need to be used for stability only. Its a thought at least
Hopefully this is something you can look in to.
Thanks and have a good christmas!