A mod read its config before it was loaded
Applies to Forge, NeoForge.
What it looks like in your log
java.lang.IllegalStateException: Cannot get config value before config is loaded.
What causes it
A mod asked for a config value before the loader had read that config file, and the loader refuses rather than hand back a guess. Server configs are not loaded until a world is, so a mod that reads one from the title screen or during startup crashes like this.
How to fix it
This is a bug in the mod, not in your setup. Update it, since fixes for this are usually quick to ship. If its config file is empty or broken, deleting it lets the mod write a fresh one. If neither helps, remove the mod and report the crash to its author.
Not sure this is your problem? Paste your log and Roastd will tell you which of these it actually matched, and what else it found.
Check your own log