Having the same thing after having loaded an 18w16a in 18w20b, happening in multiple places including a zombie spawner. My world on MediaFire @ http://www.mediafire.com/file/6mofhyqs52q3990/Underwater%20Adventure.zip . Location is (-690 17 8220) if it doesn't spawn you there already.
Michiel Kraan
Having the same thing after having loaded an 18w16a in 18w20b, happening in multiple places including a zombie spawner. My world on MediaFire @ http://www.mediafire.com/file/6mofhyqs52q3990/Underwater%20Adventure.zip . Location is (-690 17 8220) if it doesn't spawn you there already.