It's bad plastic. Basic engineering: no matter how good is the design of a structure, if the material used to make it is BAD it will develop problems at some point. That's why we sample every mix of concrete upon arrival at a construction site, to control the mix because it's that important.
Even more true with monocoque structures and small ones (like the P3), where the shell IS the structure that supports the forces and loads acting on the object, like the egg or a rocket for instance - and of course the P3 shell. It's so small that an issue with the material will show up more frequently and sooner (and with worse consequences) than, say, in a large building or something with a problem here or there. Exactly what we see.
That's to say no matter what "version" of the shell, if the plastic used for a certain batch was bad (probably the mix) then it might develop cracks at a point. The same goes for the TXs cracking out of nowhere. Bad plastic, friends. Nothing to do with screws, props, active break setup, and certainly not with the FW being used!!!
