I was playing on my 1.15.2 PaperSpigot server when I discovered a strange glitch. My friend was experiencing it as well. I decided to go into a vanilla singleplayer world and test this out. If there is a water block at y 255, and it's a soul sand bubble column, you can go into it, jump out, and you'll start jumping like you're on the moon. I think it lets you jump about 2 blocks high. If you go below y 255, it will stop. I am using Fabric, only for client-side mods. This worked on a vanilla server and a singleplayer vanilla world.

Sorry if this is a duplicate or intentional game design, I searched and couldn't find anything about it.