Shields not working correctly in Multiplayer

[Tom4tenmark]

Hello everyone, I'm having some issues on my Minecraft Community Server. It's an Arclight server on Minecraft version 1.21.1 which has a lightweight Modpack installed (I created myself) & some Plugins to make the experience a little easier for everyone. Heres my problem:

1. The Problem:

When blocking with a Shield, players don't receive damage but they get knocked back & the shields isn't taking any durability loss. Meele attacks do the same but creeper explosions are blocked completely. (So I guess they don't block any status effects?)

2. What have I tried so far:

I looked through every standard minecraft server config (bukkit.yml,...) and had a look if anything is possibly tweaking this issue but I have had no luck at all. I also tested if the problem is also accuring in my Singleplayer world with the same Modpack but once again, the problem is not accuring in my Singleplayer world, shields work perfectly fine there. I also removed all the plugins to see if it's a plugin sided issue but once again, the issue was still remaining even without plugins.

3. More Information:

Minecraft version: 1.21.1
Arclight version: arclight-fabric-1.21.1-1.0.1-SNAPSHOT-1ddfa61

I will post pictures of the mods & plugins on my server. I hope this is enough information for one of y'all maybe being able to help, thank you guys in advance!