I have an issue with the oscillation as well and I won't start a different post.
I'm flying level at FL170, the A/P is keeping track and altitude just fine, then there's about a 30 degree turn and the A/P loses maybe 100-150 ft of altitude during the turn. Speed is around 200 kts IAS, 45kts below the barber pole (shouldn't be too fast). The A/P compensates heavily for the altitude loss, starting off with VS +/- 2000 feet, then increasing the oscillations more and more until VS is +/- 6000ft up and down. This sort of dynamically unstable behaviour would end with a stall. Tried reducing power just in case but that had no effect. Had to disengage the A/P, manually level the aircraft and only then re-engage the A/P and the aircraft would continue flying level.
That's probably not normal behaviour, is it?
I have screenshots of the plane at the extremes of the oscillation and logfiles, should those be necessary for investigation of the matter.