CF's strength is high, but that only counts for the tensile direction of the fibres. In the pictures it seems the CF was not pulled on, but compressed instead (as the chassis is bent up). In the end the plate just flexed downward until it snapped.
A CF chassis should not be necessary: It may have been a bad batch of CF, but to be safe I'd make a mod. A wider top deck may help, but affects torsional rigidity of the chassis. Instead, I would try a thicker top deck, which should have a lesser effect on torsional rigidity as the plate is so narrow - and if the impacts cause the top deck to flex downward like this, a thicker top deck has more effect on strength than a wider one.
So as a first solution (if there is enough clearance) I think you could test running double top plates, much like some guys run double shock towers
