I think you're half onto something....
IMO (In My Opinion - not International Maritime Organisation, which is the top google response...

) ;
Standing in the middle must stress the boards out structurally. Plus big boards, and waves... waves have a heap of power which the human can quite easily absorb, by bending with the power / with the waves, but the rigid boards just have to prey and hope (like us when the waves get really big!). But I think big boards are preying and hoping on medium sized days.... Big boards, create big leverage for waves....

Good luck with the warranty though. Without reading the fine print, I'd give you odds of up to 1:2..... Seriously, I wish you sincere good luck !