The bug
Strongholds do not generate in certain customized worlds despite /locate saying otherwise. At first, I thought it was caused by blackstone as default block. Later, it turned out that it was not generating at all. Then, I thought it might be caused by effects being set to nether. Even with overworld effects there was no stronghold.
How to reproduce
Download the
file
Import it to a new creative world
Use
/locate strongholdTeleport there
Set your game to spectator mode
Fly down
→ ❌ No actual stronghold, but the message from /locate still says that there is a stronghold
Might be caused by the biome distribution having nether biomes. The best possible fix might be to make strongholds generation independent on biomes, but on the worldgen import.
Please provide an updated custom world file so the issue can be reproduced. The attached file causes the parser to throw several errors.