Jumping repeatedly on a slime under a low ceiling (2.1875 blocks or lower, 2.25 block ceiling works as intended), does not let the player sprintjump and get the appropriate speed, instead acting as if they are just holding w without jumping.

Attached are clips from 1.21.1 and 1.21.3 (bug introduced 1.21.2 and still present in latest I just already had 1.21.3 open), showing the drastic difference in speed spamming jump under a 2 block ceiling on slime.

I included a setup to easily reproduce, back up against the small amethyst bud, then press w + space together, repress again quickly after you land