My Cabrinha kite lines are still relatively new and I have always soaked them in fresh water and then let them dry after sailing. I noticed the other day that the one steering line is starting to look a bit frayed over 50mm, about half a meter from the kite end of the line.

1. What could be causing it?

2. How can I prevent it from getting worse?

3. Can it be repaired?

the answer is something is rubbing the lines. perhaps incorrect set up at some point?

I use cabrinha and only seen that happen where the kite has inverted on crash and been flown for while back to shore to reset the lines.... the front and rear lines crossed over at top ... make sure your lines are clear run from bar to kite without crossover in flight

i'd concur with that. tho i'm not running the same kite i have the same problem and its because my kite has inverted and i've flown it not knowing the lines have crossed over...
i think your screwed by the way. its either new lines or get your lines shortened by perrin at kiteworks. he may even be able to make you extensions to get back to the same line lend?