Bender said..
IMHO i think the nose of the board is too low to the water, Try raising you boom a bit or moving the the masrt base back a bit, This will bring the nose up and free the rails from catching.
Thanks I'll try that.. Actually I noticed later the boom had slipped to the bottom of the cutout.. I wonder how much earlier that had happened.. Maybe that caused it!
I'm going to post another topic on the mystic venom boom I have as it has a join that separates when clamped and I'm not sure if that is it's design or a flaw ( only noticed it lately..

).
I also occasionally catch a rail entering a gybe and crash. It doesn't happen very often and in short sharper chop.. I thought it might be bad technique - too sharp a foot pressure to initiate or not enough mast base pressure but could that be caused by too much board in the water? I usually lower the boom a few cms if I'm in overpowering choppy conditions..