you said you had cabon fibre sticks right, my mate has this problem, and what he had to do was when he threaded the string though and tied it, do a double knot on both sides, and about every so often just get the end of the
P.S if u want good effects get a 6 g or 10 g wieght kit and an led kit leds cost £12 and wieght kits about £9 also get a big axle for about £7 this will improve on your skills
i think it might be the henry's string that's the problem
I havn't had this problem recently as I have changed sticks but try putting alittle superglue around the string where it snaps.