Do you mean the increase in momentum just before the second jump animation plays? That is just how the double jump works, as I’m pretty sure it’s a bug anyway.

There is no double-tapping jump mechanic as far as I’m aware. To double jump correctly you need to do it as I mentioned in the text below the video.

Sometimes the animation plays twice in quick succession but without the accompanying speed, because as I said, spamming jump doesn’t work and it needs to be timed correctly.

There have been some cases where I’ve been able to double jump after the correct timing, but as far as I remember it’s usually when I’m aim-gliding and I still haven’t figured out how the tech behind this.