Out of curiosity, what bait/lure were you using and what line class? Might have been a trevally, kingfish or even a jew. What is your guess?
The sinker should not have frayed the line. Check all your guides - this is the most likely cause. Use of piece of nylon stocking and see if it sticks or frays when it goes through each guide. Also check the lip of your spool and also the line roller and make sure it is working. Was the line frayed all the way along, or just the bit nearest the fish? Could it have gone over some rocks or around some timber.
Platypus line is good, but a bit stretchy. I used to like platypus pink, but it is no longer IGFA rated so I don't use it anymore. I am now trying Hawk tournament and so far seems OK.
Jeremy