Structure-Nesting not working in the new snapshots (2021.1 pre-releases)

[LightmareShadow]

I have a mod which used to be in the 2020.5 version. It had a work in progress Mega-Dungeon structure, which used one structure that would spawn multiple other ones around it. These used to be picked from a couple random options as well. However I was yet to finalize the procedure that handled this. I later moved the structure to the pre-release, where the middle structure stopped spawning structures around it upon spawn. I tried redoing the procedure, simplifying it to the bare minimum for testing purposes and making an entirely new structure spawn, but no matter what I did only the middle room would spawn. This might have happened due to the transferring of the project from 1.15 to 1.16, thought I didn't use custom code for said structure. Is this a bug? Or has the way to do such structures changed?

Here is the workspace if you want to test it out. The structure is called Mega-Dungeon, and procedures with names that contain it's name are about the whole structure nesting technique. You can try and bump up the spawn rates, the middle structure is this corridor esque room with an invisible entity wearing Iron Armor and weilding an Iron Sword. Not to be confused with the circuler structure also found in the surface's underground.
BackupNumber14.zip

[KlemenDEV]

Duplicate of #925, #686, #963 and https://mcreator.net/tracker/issue/64908