I have a HHX and have used it about 5 times, with similar results. I find that if I tie the normal HH hitch, following @Richard Mumford-yoyoman instructions that no matter how tight I tie it, once I'm 20-30' up in the air the hitch/rope stretch out enough that it no longer grabs when I load it, making for some interesting moments. I primarily use it for rec climbing (Rope Runner is my preferred device with Rope Wrench in 2nd place) and normally just footlock up with just the HHX and neck tether. So, when the hitch doesn't grab upon unloading, there is nothing stopping me from sliding down the rope quickly other than my hands on the rope. If I tend the hitch it grabs of course but that requires taking one hand off rope, holding myself up by one hand alone until the hitch grabs, which is doable but seems unnecessarily difficult.. If there is a crotch I can stand in and lanyard in, I re-tie the hitch aloft and after this first redo it always works perfectly. I've tried weighting the hitch by sitting in my saddle while still close to the ground and every time when I get high enough for it to be annoying to come down just to re-tie, it loosens on me. I'm using it with the supplied 8mm hitch cord on Samson Vortex and tying the hitch with 5 wraps. Any insight on what may be the problem?