The other was a Master Airscrew three blade and the entire blade came off, my neighbor found it in his garden the next spring..The Tru-Turn spinner on it was flattened out like a mushroom.

Inverted mounting makes hydrolock a very strong possibility and combined with any manufacturing defects/weaknesses - I'll place my bet there.

Why did it die the first time - rich or starving for fuel? Any chance the engine was choked partially or completely by accident while cranking? Was the tail raised while carrying it? Myriad possibilities. But it is still a surprising failure. I agree the metal looks thin in the photo on the one side but whether is it nominal or a visual trick of the photo cannot tell of course.

Bummer.