Hi Robbo,
Bridles snapping is not a new problem, The Wipika Airblast back in 2001 used bridles to assist in relaunch and they also snapped after time.
The answer to your question the answer is NO, they do not show signs of wear before they break, but you can check them by feel.
The core strands are the main tensional strength of the bridle and the woven outer is more of a protective sheath. The core strands will break and leave all of the load to the outer cover which is not designed for load.
To check, simply find where abouts the lines run around the pulleys and using your forefinger and your thumb, pinch the bridle line and pull it through your fingers, a broken core will show up as a skinnier piece of bridle. You wont see it, but you will feel it.
Bridle life can be extended by washing your bridle lines in fresh water after each use, or having failed this idea, keep a close finger on the bridles and be prepared to replace them before they break, Oh and if you break one, immediately replace both sides as the old one will be stretched and about to break and the new one will be fresh and tight.
I strongly advise all bridled kite flyers to check their bridles every other session after the kite is a few months old, depending upon level of use. I can speak from experience as a line snapped on my old Wipi AB 6'3 at around 25 feet in 30 knots of wind and I inadvertantly did the worlds first kiteloop and landed on my back hard enough to think I was dead!

I hurt for ages and thought I would cough up or pee blood

Hope this helps,