Issue description

These 3 mods

Crashing only on dedicated servers, not lan multiplayer.
Removing one of them (no matter which one) solves the issue.
I tried no mixin version of the SecurityCraft but not solved the issue.

Steps to reproduce

No response

Script used

Nothing

The crafttweaker.log file

https://pastebin.com/NNtRbPb1

Minecraft version

1.12

Modloader

Forge

Modloader version

forge-1.12.2-14.23.5.2860

CraftTweaker version

CraftTweaker2-1.12-4.1.20.700

Other relevant information

No response

The latest.log file

https://pastebin.com/Su39BHsv

This does not look like an issue in CraftTweaker to me.
During the load cycle, builds an internal registry of all existing items so that it can later resolve brackets like <minecraft:iron_ingot> into a proper itemStack.

When it asks the Vertical Slab Item for all variants it has, that call errors.
From the error log it seems to me that some versions of Forge don't match with each other.
Try downgrading to e.g. 14.23.5.2854 (which is what the DoubleSlabs mod was built against).

Also, that issue has already been raised on DoubleSlab's side:
CJMinecraft01/DoubleSlabs#277

This is most likely an issue with DoubleSlabs calling a client side only method in a non client side only method, so when we call the method, it crashes.

There is nothing for us to do to fix this, they need to fix it.