4 months post ACL, knee has jolted when I walk

I am trying to walk without a limp, and I just went for a walk and my knee has jolted twice... I am really concerned maybe I have torn or the graft has snapped

It is when I get to land and my leg is more straight, I am consciously trying to walk with proper gait but when I do eventually it jolts 😭😭😭

Please is this a lack of quad strength of what? It's like it's hard to hyperextend the left leg completely straight, I can do it but for example if I'm on one leg balancing, I can't do it as it feels like it'll snap?? Or like a double jointed thumb is a way to describe it