Horrible form. First video you didn't *complete* a single lunge. Second video you completed 6 lunges on your left foot forward, and two on your right foot forward. You're going to develop a massive imbalance if you keep it up.
1: *always* touch (not bang) your knee to the floor.
2: *always* step forward the exact same distance on each leg, for each step. Put tape on the floor, use chalk marks, step on seams on the floor, whatever, just make sure each lunge is the same distance.
3: Don't pause between steps. Do you stop with your feet together when you walk? No? Then don't do it when you do walking lunges either. It's walking lunges, not line-dancing lunges.
4: Don't lean forward. Back straight and straight up, arms at your sides, weights should be at your hip. You're leaning forward too much, and you'e leaning forward at different angles for each leg, so yet another source of imbalance.
5: 5 reps per leg? Drop the weight to 20 kilos and do 20 steps, 10 per leg, with perfect form. If you can't control your knee touch and it bangs on the ground at the end of a set, lower the weight.
