It looks like this mod didn't supported the mods which add other dimensions that using Overworld's world-gen rules (Such as Multi-world and Overworld Mirror)

Because some player started in superflat world and they can't explore the world because there's only one biome and no resources can obtained, So they using these mods to created a second dimension world to explore, But the AW2 structures and NPCs didn't spawn in these dimensions...

Maybe add a config to enable world-gen in other dimensions will coming handy...

Sorry, but AW2 does not touch or spawn anything in dimensions that are not the overworld. This is not something we will be changing and there is no overall config setting for it possible.