Hello! This issue was originally reported on my tracker, here:
EnigmaticaModpacks/Enigmatica2#160

Issue Description

The server crashes on startup

Mod version

1.12.2-2.6.1.390

Crashlog

https://hastebin.com/vadolijini.rb

Did you figure out if it was AI improvements that caused this issue?

Oh sorry, I forgot to report back. It wasn't AI Improvements, I believe it's a rare issue with certain operating systems, definitely not a mod issue.

This crash basically means that AW doesn't have access to a java class that normally is fully accessible. And only core mods can change the accessibility of the class so only explanation I have is that one of the core mods that you have there messes with the vanilla code which then breaks AW. If you can limit this down to what core mod causes it I can take a look, but then my likely follow up will be to have them fix their logic or remove that mod from the pack if you want to use AW.

Alright, thank you :)

Oh, I bet it's the mod AI Improvements that changes it.