umm not sure on cause,
as the frame was broken when i bought the boat,

I suspect that the hull had been hit by something as it looks like it has been repaired but they did not notice/fix the broken frame...

We simpley took the deck off pulled out the old frame and replaced it with 10mm foam sandwich fiberglass frame... however the old frame's had big air-flow holes in them - maybe this is why mine broke and came lose.