Sharp Bouncing

The fact that you get the problem at higher frequency bumps rather than lower frequency bumps makes it sound like you have hit some sort of resonant frequency that your dampers aren't handling. Maybe try to find a piece of local road that induces it, then try different adjustments on the dampers either way to see if one of them improves it. I.e. don't just try making the dampers firmer, try making them softer too.

It could be that the resonant frequency of bounce of the tyres (which probably relates to their pressures) may be hitting a frequency the dampers are failing to damp.

Steve.