Good catch!
I don't understand why i'm the first to notice it. The first time I watched it I noticed it jumped and I thought it was just a glitch in my data stream.
I went back and watched several times, and it did it every single time in exactly the same spot. I thought it was peculiar that the video would cut forward so suddenly as she was about to take her first step onto the landing.
I expect she stumbled, and they simply cut out that section.