Essentially, I can't get my structure to spawn in at the spawn point of a new world when it is a void world.
My other worlds have their structure spawn in perfectly, but for some reason, it doesn't like void worlds (since there's nothing for it to be placed on).

I tweaked the setting a little, such that I managed to get /#gen <structure_name> to work by setting the height to sea level and removing the average height map check. This allows the structure to spawn but at y=1 (not even at sea level, unless super flat has its sea level at 1?).

So I added a load of air/blank blocks underneath my structure and using /#gen it generates perfectly. But here's where the problem occurs, when you reset the world, the structure DOES NOT spawn in; I have to /#gen it.

So it turned out, when I made the dimension I turned off "MapFeatures" so that villages etc. Didn't spawn and it was a truly void world. But, I didn't set Recurrent complex to ignore that setting.