The bug:

While sprinting and holding down the jump button at the same time, the sprint animation plays at a slower speed, causing movement to appear floaty and weightless. This doesn't occur if the player presses jump each time they come in contact with the ground after jumping.

How to reproduce:

In 3rd person view, sprint and hold the jump button at the same time.

Sprinting while holding jump: Minecraft 2021.03.06 - 15.02.04.11_Trim.mp4

Sprinting while tapping jump: Minecraft 2021.03.06 - 15.02.04.11_Trim (2).mp4