I've had it happen with dacron strings too. I think the brass nock point I was using then may have contributed to the problem. That is one of the reasons I quit using brass nock points. I just tie in nock points with B50. They are easy to move by twisting them up the string. Once I have them where I want them, a dab of superglue locks them in place and makes them last longer. They do wear out, but it's cheaper to replace them than strings.
I make my own strings, so I probably replace them more often than most folks. If they get to looking a little ragged, I make a new one.