Hey bud, take a picture of your set up right before you put weight on it. It may be as simple as you haven't tightened the hitch down enough yet. This would consist of take those two ends of the hitch cord that go to your caribiner and working the slack out of them until the line is tight. While keeping it tight, go ahead and apply some pressure to the hitch. I have noticed that with certain hitches they need to be tightened up as I call it before you go about your business. I would consider this just part of the territory in using hitches. Once you weight it completely it may be a little tighter to undo but should ultimately returned to that locked position easily in the future.
If you don't mind sharing how much do you weigh? Since they are friction hitches you may need to add a wrap if youre a full grown man. If you are going to add a wrap I would suggest doing some reading and become familiar with the hitches intently before climbing with them. Just because you bought a set up tether from the store does not mean it fool proof.
Lastly, I still prefer a prussic for my tether. It to me bites harder than any other hitch. There's just a little getting use to it and you can undo it and move it up and down very easily. I may try to get a video of that for you to consider.
If you go the retie or add wraps method check this video out as a starter