This is why the biomes are currently disabled. I have no idea why this occurs. I'll take a look at the placement algorithms themselves.

If the fix was datapack features, could this reasonably and easily be backported to 1.18.2? I just noticed this and my heart sank because the amaranth biome is one of the biggest reasons I downloaded the mod. Please backport the fix...

No, sorry, I have already tried and failed because of Fabric API bugs. Furthermore, I am constantly moving forwards and will not backport to older versions. The Promenade experience in 1.19 is pretty much complete and still growing.