One thing we know for sure is that the primary suspension issue has yet to be dealt with - there were a couple of slow motion shots last night where you could see the 28 porpoising for quite a while. Hopefully there's a full-on fix for that scheduled for Spain. Frankly, I'm not sure how Button is dragging that thing into good points paying positions right now, but hopefully he will have a car that can fight for wins soon.
In the post Malaysia Peter Windsor "Racers Edge" video, Scarbs tends to think that the most significant problem is its sensitivity to ride height and pitch. It has a narrow ride height window (where it provides good downforce). This means they have to limit the the up/down travel. They would like to soften the suspension (and get better slower corner response) on the front, unfortunately the travel would take it out of its current operating window so they can't.
So they deliberately "nail" the front suspension, which works for most of the circuit , but when the front end encounters bumps the tyres act like balls bouncing up and down with little damping. Not only that, as it bounces the front floor feed keeps opening and shutting.
If the "narrow ride height" theory is actually true, the will have to revise the aero front part of the car to widen the ride height window, which means front wing, nose?, turning vanes, barge boards, floor, side pods etc. Once they have achieved that they can soften up the suspension.