Interesting. I have seen a similar failure on a P19. In that case there was a bang, I looked up and I thought I saw the mast was bent and it held for a "second" and then broke(later I figured I was seeing things). In that case the diamond wires were brand new dyform. We assumed the wire slipped in the fitting but the rigger cut them and there was no slippage. There was a small difference in the diamond wire length.

I have heard of a another case on a aluminum masted non spin Tornado where the mast bent. Also new diamond wires.

In both cases, no one determined what happened. The theory was something slipped but they could not find anything.

There was another case that was not quite the same but I have always wondered about it. I was sailing an Aluminum masted Tornado in 10-12 kts with brand new dyform diamond wires. We had a perfect port start but then boat would not go. P16's were passing us. Then there was a bang high up the mast and then the boat started sailing normally. There was no damage to the mast and no indication that anything "hung up".

In all cases it was probably the first time we really cranked down hard on new diamond wires with a pre-bent mast and something slipped. I have wondered about whether I would have broken my mast if the wind had been higher.

I know I am not offering a solution, but maybe you can find a common factor.

FYI, I use solid wire, where I can, for diamonds now.