Hi Neb.You need to have the chest mount really tight or it wobbles and there is only so much the gyro can do.
You also need the camera attached to the chest mount with no extension pieces as it just increases unwanted movement of the camera.
I have the chest mount done up as tight as it will go, with the chest strap of my rucksack as tight as it will go underneath the camera as a brace.
A video from last year!