I know from #46 that it was necessary to re-implement Mansions, but there are a couple of ways in which Lost Cities mansions are different from vanilla mansions beyond just the /locate command:

First, they're generating in arbitrary biomes. In vanilla, Mansions only generate in the Roofed Forest biome, but they seem to have no such restriction here. This is resulting in some weird things (and I suspect they're generating more often than they should as a consequence).

Two, because the vanilla 'Mansion' feature isn't generating in the world, the Cartographer villager cannot sell maps for finding Mansions. This actually cuts out a key vanilla mechanic for progression.

I don't know if you can fix the second, but the first definitely should get some attention.

This is MC 1.12.2, forge 2501, Lost Cities 1.0.1, BiomesOPlenty-1.12.2-7.0.1.2298. Plus other mods.

Hm. Doing minimalist tests, and it might be a mod interaction issue for this and #53. Will report again soon.

Found the problem. Reproduced with JUST forge 2501 and LC 1.0.1.

Made only this change to the default profile:

    # List of biomes that are allowed in the world. Empty list is default all biomes. The factor controls how much that biome is favored over the others (higher means less favored!) [default: ]
    S:allowedBiomeFactors <
        plains=1
     >

Create a world with seed: -8211488617467187250

Load in the world, experience the wonderful sound of guardians in a plains biome right next to spawn.

There's a mansion not too far away with a monument under it:

So it looks like simply adding anything to allowedBiomeFactors breaks the biome checks for monuments/mansions.

I don't know if this is also the case with cityBiomeFactors

For clarity: I completely stripped the Config directory first before making the above edit, and Lost Cities is the only thing in the mods folder. So I'm confident this is just a Lost Cities issue.