Anti Levitation not working

[areyoureal]

Minecraft ver. 1.21.1
Aristois build 527 Donor edition

Anti levitation is not functioning in 1.21.1 singleplayer / multiplayer.
Being hit by a shulker projectile makes the player float.

However, applying levitation effect via commands and then being hit does not cause the player to float.

Recording available if needed.