Extending off of what theturbosoggy said on Curseforge: when in water, lava, or powder snow (or when under the influence of blindness), the skybox renders.
Deleting the sun, moon, stars, and sunrise/ sunset sky when in these situations might fix this.

hm, i guess i never made a check for if someone was in water or lava.

Is there any reason this won't be fixed?

Agreed, why cant this be fixed?