I'm currently troubleshooting trough trial and error...
Edit: I've been trough a lot of numbers and settings but can't seem to find a cause. Distribution (Placement) and Tree Height Placement Limit don't seem to have anything to do with it.
Edit #2: The trees spawn on top of other structures. It might have something to do with the placement order but I can't change that since it has to be in a specific feature step. Also, since I added a third biome to my datapack, every world I create with it crashes the game because of "Feature Order Cycle Found". I have no idea what this means...