The Poison effect doesn't exist.

Version: Fabric 1.20

Mod Version: 1.20-2.1.5

Only seems to happen in 1.20 and 1.20.1 servers
This issue isn't present in 1.19.2 and 1.8 servers for example.

Weird. What happens if you click or hover on the poison effect in your inv screen when you get it?

Hovering makes the effect have the description and color hex code.
Clicking does nothing

I think I left it in the cinfigs or tag. There was one of those where you can add effects to blacklist

I too have this problem but I’m on Forge 1.20.1