Well Pirelli have released their report and eluded to that it must be a parameter on the tyre (pressure or temperature) that caused the failure, however the sensors showed nothing outside of the parameters they set. So the likely conclusion is either:
a) Teams are doing something similar to Ferrari's fuel flow sensors, which can bypass the pressure sensors providing readings to reduce tyre pressure, OR
b) Pirelli tyres are trash and they require a redesign to increase structural integrity, or in the meantime, provide higher pressures within the tyres.
I wonder what the drivers will think in all this. Failures at 200mph on a street circuit are hugely dangerous and I'm surprised Max and Lance came out of both incidents unscathed, albeit shaken in Lance's case.