The bug

When a player jumps into an opening shulker box, are moved horizontally by the shulker box and stay floating until the opening animation of the shulker box ends.

To reproduce

1. Place a shulker box on the side of a block, so that it is at eye level with the player.
2. Jump, and while midair, open the shulker box.
   → The player does not fall while the box is being opened.
3. When the box finishes opening, the player falls.

Video

Here is a video link of the bug being recreated in the 20w17a:
https://youtu.be/ArUFmQwZd-8