Hello, not CT obviously but I used to do the same. Your whole body is moving around forward, your glutes are not contracted and your pelvis is tilted forward. Your back is excessively arched to compensate. For instance, on your second vid, reps 3 and 4, you are so much forward it's obvious you're using energy to try to balance yourself.
Try the next times, to squeeze your glutes as hard as possible the whole time. You can use a slightly wider stance, or point your toes a bit out to help you mobilize and feel them. Also brace the shit out of your abs.
Personally I don't do much glute work for they are huge from my lineman years, but I would recommand, as your warm-up 3 sets of 15-25 glute bridges and clams, to really help you feel your glutes. Then, Sumo deadlift, pull-through, mobilizing your glutes correctly during deadlift, lunges. You can also try hip thrusts