Here's a similar bug as MC-184740 .
Swamp hut and Monument seem to be invalid structures and cause mobs(e.g. witches, guardians) not to spawn. Other common mobs spawn instead.
However, Nether Fortress and Pillager Outpost seem to be working properly.
Related issues
duplicates
Comments
galaxy_2alex
migrated
Thank you for your report!
However, this issue is a Duplicate of MC-186096.
Please use the search function in the future to prevent duplicate reports.
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