I've been using my guardian farm in 20w20b because it wasn't spawning any guardians since 20w21a and when i updated to the pre-release it still doesn't work
Linked issues
duplicates 1
Comments 2
Your world is broken and needs to be repaired manually. See MC-186096.
You will need to either reset the chunks or "re-assign" the monument structure to the area where it should be, once this data was deleted in 20w21a it won't magically reappear in the data of the world, reffer to MC-184740 for more information about this issue.