Describe the bug
When trying to boot up any world, I get a server error, despite only playing singleplayer.

To Reproduce
Install both Hexcasting and Spectrum, along with all of their dependencies.

Expected behavior
A concise description of what you expected to happen.

Minecraft version
1.20.1

Mod version
1.8.2 at the time of finding this bug. It persists into 1.8.3, which I am uwsing now.

Screenshots

Crash Report
https://mclo.gs/eQswcnt. Not a crash report, but still something that may help.

I'm not having this issue, is it possible that other mods contribute to this?

Could try a binary search (ie remove half your mods, see if the issue is still present to determine which half has the problem, repeat until you narrow it down)

I'm not having this issue, is it possible that other mods contribute to this?

I definitely think this is the case. The problem is, I have no clue what other mod(s) could be causing this!