I've adding dungeons mods to server for a easy looting in multiworld and figured actual problem with mod Roguelike Dungons https://modrinth.com/mod/roguelikedungeons/versions?g=1.20.1
The dungon can't spawn properly in multiworld dimension, and i think because it can't load data from world/data/roguelike.dat where dungeon structures is located. Something is missing to ask for structure in your mod i guess. And maybe other structures mods may be not properly loaded.

Issue i think can be closed for now, Roguelike Dungons mod developer made his own fix, i guess the problem was in his mod. Best wishes