Agreed on crypts being fairly sensitive (though crypt wendtii isn't so much), and also that the lud generally isn't. The only time I've had a massive tank melt is after doing a 50% water change with water that was especially warm. It was a crypt-only tank, and they all bounced back. Any chance you did this too?
I also agree, by the way, that you should avoid giving crypts funny looks, as well as telling bad jokes or swearing in their general vicinity.