Sounds like failure of "structural plastic." With those saddles does the kayak get strapped down to the saddles rather than to the crossbar? With my older Thule saddles the strapping goes under the crossbars, which means that if they stay on the roof the boat does too. Normally I don't use bow lines but don't assume because I do it it's OK. (Mandatory safety warning) I do often double up on my cam-lock straps, having heard about buckle failures and noting the rust on the ferrous pivot pin.

Good pictures of the damage. It doesn't look like it will be too hard to repair, although it may not be invisible.

Mike