Of course it's the worldgen. Trying to set up a flat world at a certain height was not trivial. There's no reference for all the generator settings, and for a flat world, one actually needs to use the option marked as deprecated ("HeightGen" is "old relict" in the Book), with undocumented settings ("FlatHeight"). Only after fiddling for quite a bit I found out there's an example for Superflat world in the Book after all.
Another pain was disabling the mobs. Just deleting the [Monsters].Types line did nothing, which at first startled me, but then I figured out it was getting replaced with the default. I guess there's not much we can do about this one.
Finally, I failed hard at setting the permissions. It's easy to debug plugins if one is an admin on their own server. However, to set up regular players, things are super complicated. First I had to find out what permissions even to give to the players. The newer plugins have a Permissions table which lists all the permissions and their recommended groups, but it's not for all. The Core has a long list of permissions with very little recommendations. Combine that with the need to re-rank in-game players for the permission changes to take effect, and it's a mess.
Another pain was disabling the mobs. Just deleting the [Monsters].Types line did nothing, which at first startled me, but then I figured out it was getting replaced with the default. I guess there's not much we can do about this one.
Finally, I failed hard at setting the permissions. It's easy to debug plugins if one is an admin on their own server. However, to set up regular players, things are super complicated. First I had to find out what permissions even to give to the players. The newer plugins have a Permissions table which lists all the permissions and their recommended groups, but it's not for all. The Core has a long list of permissions with very little recommendations. Combine that with the need to re-rank in-game players for the permission changes to take effect, and it's a mess.