Creating a warped forest superflat world with decorations freezes

This preset gets stuck on 0%, with the diagram on the loading screen looking like in the image below.

 minecraft:bedrock,2*minecraft:netherrack,minecraft:warped_nylium;minecraft:warped_forest;decoration

A world with the alternate preset

 minecraft:bedrock,2*minecraft:netherrack,minecraft:warped_nylium;minecraft:warped_forest;

generates in a reasonable amount of time, but lacks trees.

Possibly related to MC-171020.
EDIT: Crimson Forest and Soul Sand Valley superflats not tested.