An oscillating pitch and speed calls for an immediate hands ON(if not already ON) and if there is obvious unstability,the auto flight must be disconnected.
Such issue may be avoided by capturing the glide at the correct altitude....(glide starts at 2500 feet,dont capture it at 6000)..
Such oscillations should be reported by pirep and deviations reported by SRS.
Airlines aware of such deviations should plan extra sim to ascertain such pilots manual skills.