https://pastebin.com/0aYEt4kN
It says something about Blood Magic in the crashlog, but we do not have that mod on our modpack.
If you need more than that posted in the pastebin, please let me know.
We are running sponge on this server.

https://gist.github.com/forestbat/1f8d89e052460debabda5c55ae9106f4
I also met the problem。

For some reason it is still trying to pull in some BloodMagic code, when it is not installed.
I can replicate this and I'll try to work out what I've done wrong.

6f6168a
I've released 1.12.2-1.2.1 which includes this fix, which I test with and without BloodMagic.
So fingers crossed this fixes it for you.