I had a problem with this, on this trick… for a while.
Make sure you keep your string taut. If there’s any slack in the string when you do some of the maneuvers, the yoyo will eat up the slack like there’s no tomorrow.
So yeah. Keep your string nice and taut/tight. Try doing it a little faster, but also try pulling your hands apart as you do the motion. Pulling your hands apart will ensure the strings are taut while also helping the yoyo naturally do the motion.
Doing the hop up into the top string after double or nothing and then immediately going into the 1.5 mount helps with the snagging. I used to have this issue all the time. If you do the hop up and go straight into the 1.5 mount you shouldn’t have this issue anymore!