In my limited experience of multirotors I've found the 'wobble' while descending very common if not universal. It's caused by the rotors descending into their own prop wash. In helis it's called '
Vortex Ring State', in real helis is very dangerous and has caused many fatal crashes, in RC helis it's not usually so bad because they have enough surplus of power to 'punch out'. Multi rotor props also have enough power to 'punch out' of VRS but as they do you get the wobble.
The only 'solution' i found is not to descend quickly and/or steeply. You either descend while flying forward (thus leaving the prop wash trailing behind), or you descent very slowly. You may be able to reduce the effect slightly by tweaking the flight controller settings, but you arent going to get rid of it because it's an aerodynamic phenomena which electronics cant prevent.