Don't know if it helps, but apparently the lighting level (brightness) in the room affects the Tobii 4C. I could be flying in ED all fine, then the screen just suddenly jumps about for no reason. My head hasn't moved, my eyes haven't looked anywhere else.
Then it will settle down on its own after 1 or 2 seconds.
The only explanation I can offer is probably the lighting levels in the room changed and Tobii lost track - the same way it loses tracking when I put my hand up to scratch an itch on my cheek (nowhere near the eyes).