worldgen advice

ive been trying to create a custom dimension, but currently im stuck on one specific feature. its a vegetation patch with a random selector feature that creates one of three options, huge red mushroom, huge brown mushroom, or mushrooms on the ground.
its not generating in the world, and i cant figure out exactly what the problem is. it works fine without the random selector, but that just generates one feature. ive tested all three possibilities this way, and they all work individually, but not combined. the /place feature command also works fine, even with the random selector, and i dont understand what the problem could be.