Nock 2 It Issues

[RedBeard22]

Has anyone had issues with their Nock 2 It? I got the non-travel adjustable one about 2 weeks ago used and it's let go of the string mid-draw twice in the past week. I thought the first one was my fault (maybe I bumped the barrel with my thumb) but I tuck my thumb behind the barrel and the first thing I checked when it happened the second time was my thumb position-still behind the barrel. The thumb barrel weight is not too light. haven't been able to replicate it with a string on a door hinge. It seems almost random.