I've created a datapack with some custom dimensions and custom biomes. the biomes are organized by color and use a surface builder coded with that color concrete. when I load this datapack, everything works fine: the concrete and biomes match. however when I save and quit, and reload, all generated biomes get swapped to something else. they still use the original surface builder as when it was first generated, but the biome colors no longer match the surface generators. pretty game breaking issue, as biomes should be consistent and shouldn't change when you reload.

upon first loading the datapack, this is the purple biome. it uses purple concrete on the surface and has purple fog and particles.

however, upon reloading, this biome is now yellow. the surrounding generated biomes have changed to different biomes as well. new chunks don't seem to be affected, but all chunks generated will change on relog. the biomes appear to have the same borders and follow similar rules, IE all purple biomes will be yellow (unconfirmed if this is the same across multiple save files).

Pretty gamebreaking issue for custom dimensions, hoping we see a fix for this soon.