Sculk Shriekers and Sculk Sensors are generated at random times with the "/placefeature minecraft:sculk_patch" command

What I expected to happen was...:
All the sculk stuff would generate with the command every time I type it.

What actually happened was...:
Sometimes Sculk Sensors and Sculk Shriekers don't generate

Steps to Reproduce:

1. Create a new superflat world with cheats
2. Copy & Paste "/placefeature minecraft:sculk_patch_ancient_city or /placefeature minecraft:sculk_patch_deep_dark " into the chat 
3. Observe 
4. Go away from the generated sculk
5. Keep repeating the same steps from 2 to 4 a few times then stop.