Mirages/Incorrect distant terrain

Warning, this is a dumb help post. I don't really have much idea what I'm doing; bear with me.
I want to use Distant Horizons on a custom map created in WorldPainter. In the software, I did terrain height and biomes, but nothing else, leaving all other aspects of generation to Minecraft.
I've used Chunk-Pregenerator/Chunky mods to preload the world, but both have the same effect shown. Terrain in "LOD/Distant"(idk the term) distance, where it's handled by DH, doesn't match the actual world; it renders what the world would look like if wasn't custom, instead using the seed. Attached image shows a sort of 'mirage', where a floating island biome that doesn't exist fades in and out of existence.

Occuring in Singleplayer worlds, Minecraft 1.20.1, Forge 47.4.0, attached is a modlist and latest log.
Also yes my vertical render distance scale is 100%, and my horizontal 0%.
Screenshot_124.png
Screenshot_125.png
latest.log472.05KB
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