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!

latest.log
Hopefully this log isn't cut off after 25000 lines. How do I re-open an issue?

You may (or may not?) have had a button next to the "post" one.

I will take a look tomorrow, thank you. Log reading on phone is pain.

The Modonomicon Guidebok API, as well as Tinkers have issues sending stack nbt data over the network and therefore you can't join the world.

Something in your pack messes with nbt / network packets. Your guess is as good as mine, though.

Try removing mods that are not Modonomicon/Spectrum/Tinkers aka. Hephaestus until the issue goes away. Once we find out what mod exactly does these modifications we can narrow down the cause.