Some Structures generated pre-20w21a still have no valid Spawns respective mobs

What I'm asking is, does this also happen if you upgrade from 1.15.2 directly to 20w22a? Because otherwise this could just be because the last snapshot corrupted your world save data.

Ahhhh I just loaded an older world into the new snapshot and the guardian farm works. I think the corruption that you've referred to may be correct. Is there anyway to fix this, even just the structures with the farms at them?

But also how is that two of them got corrupted but not the wither skeleton farm, shouldn't all previously generated structures that had been in 20w21a have corrupted because each of those locations was visited in the snapshot.

I loaded in Pillager Outposts and Witch Hus in 20w21a too to see what happens and both of them gave spawns even though I'm not sure about witch since it might've been a random spawn by a slim chance since it was night when I tested it.

Pillager Outposts and Nether Fortress mobs spawning again as normal, Only Monuments still don't. Updated from 20w21a

I can confirm, pillager outposts working again, but witch huts are still spawning zombies, creepers, skeletons and spiders, but no witches. That's going from 20w21a to 20w22a

Yeah, I have reported a time ago something similar, but I didn't knew that my bug also applies for Overworld or End.

This is one of my reports: https://bugs.mojang.com/projects/MC/issues/MC-184311?filter=allopenissues

And here is another related to the other report: https://bugs.mojang.com/projects/MC/issues/MC-184308?filter=allopenissues

If Mojang staff see those 3 bugs. Probably those bugs could be the same bug. See the three reports please.

same with me for all 4 farms. seems across the board nether fortresses and pillagers are fixed, but witch and monuments are not. 

Yeah, this is a serious problem (and I was the fisrt to report this with explanation, and I'm happy 🙂 )

I tested upgrading from 20w20b to 20w22a and both nether fortress and monument works fine, however upgrading from 20w20b to 20w21a an then to 20w22a seems like doesn't work the monument, but the nether fortress work just fine. I don't know about witch huts. (sorry for my english)

I updated directly from 20w20b to 20w22a and Nether Fortresses, Ocean Monuments, Pillager Outposts, and Witch Huts all work as intended. Seems to be an issue with corruption caused by 20w21a.

I agree that this may be corruption caused by 20w21a. I updated my server from 20w20b to 20w21a, and they're not working.
Tried to back-port a world generated in 20w20b, updated to 20w21a, then back but nope. They won't spawn in the monument loaded in 20w20b originally, even on 20w20b. Nor does it help to update to 20w22a.
Was hoping back-porting then updating would be a viable workaround, but alas no. Damage was already done by 20w21a.

Created my server in a snapshot(dunno which) then never skipped any snapshots. All structures work except the monument. Even then, the monument is still recognized by the /locate command

If you have upgraded from 20w21a, and this issue is happening, your world is probably corrupted and therefore mobs no longer spawn in these specific structures. You can fix your world manually, I believe there are some instructions in MC-184740, but it's a bit complicated.

Note that snapshots are made for testing – world corruptions are to be expected, and upgrading the world won't always work.

If you encounter this issue after upgrading a world from 1.15.2, or if you encounter this issue in a newly created world, please leave a comment here so that I can reopen the ticket. In this case, it is a valid bug.

I made a guardian farm in snapshot 20w20b, and then updated to 20w21b and it stopped working, Today I updated to 20w22a and it still wasn't working. I trid optimizing my world, and it didn't work, so I can't revert to 20w20b and skip straight to 20w22a. So would the only solution be to fix it manually, or should I wait for the next snapshot?

hello mod, yes, this happens for worlds created on 1.15.2 to 20w18a. (Every version before 20w19a.)

This is confirmed by my ticket. Note, my ticket is only for nether, so how I said, Overworld and End are also affected.

My report: https://bugs.mojang.com/projects/MC/issues/MC-184311?filter=allopenissues

Also I state, Bastions can generate Zombified Piglins, which is not supposed to happen.

@Joaquin: You issue relates to the /locate command not working, and does not expand to mob spawning.

Is there any intention for Mojang to fix this by writing a script that when the chunk with old structure is loaded it will fix it's double tag problem thus fixing the structure?

Well i tried going back to 20w20b, but the corruption from 20w21a is still present, so i reloaded a backup of 20w20b but it would mean losing over a week of progress (guardian farm was not built yet, witch farm not built yet, several portals to overworld locations not created) etc etc. So either way i am stuck with building a fresh Witch farm AND Guardian farm either way i go, unless Mojang fixes the issue in a snapshot, but by the sounds of it the world is corrupted and can't be fixed that way. I read the post on a possible way to fix it, but it's WAY too complicated to bother.

The bug has still not been fixed. My witch farm still has regular mobs spawning inside. 

To mention, the solution on the previous issue works fine, but yes it's complicated. A more simple way of dealing with would probably be using a region editor, such as MCASelector to delete the chunks containing the structure. This would also mean loosing the farms themselves but the structure will generate its mobs again.

Don't use MCA Selector to delete the chunks, if the chunks were created in a previous version of world generation, you will end up with completely different terrain when you regenerate it.
This is what i got when i deleted the witches hut
https://i.imgur.com/BRYMxV6.png
Snowy Taiga took it's place, in a swamp, lol
Thankfully i made a backup of that world before i deleted the chunks, and hopefully mojang can fix it in a new update or something, afterall they fixed the pillager outpost spawns which were broken in 20w21a, but working again in 20w22a

The issue was resolved for pillagers and nether fortresses for me, however guardian temples and witches are still broken. It doesn't really make sense for some structures to be fixed and not others, unless someone made a huge blunder in their coding structure.

FWIW, I was unfortunate enough to go through 20w21a which effectively emptied my ocean monuments (a direct 20w20b backup to 20w22a transition worked OK). So I had a look at my regions and noticed that for certain duplicate references with both lower and upper case versions the former didn't have the data of the latter (as already mentioned). So I located all mismatches (79) and copied the data manually. After that I upgraded this 20w21a world to 20w22a which resolved the issue for me, more guardians than you can shake a stick at.

The only side effect is that one elder guardian relocated to a different underwater structure in my neighbourhood. I guess I can live with that 🙂

Yo wait, Marko Lukat, I'm not sure I'm reading this correctly, was this process fast? Were you able to search for the structure files? Did this only fix that one structure or was it all of your broken structures? What file editor did you use? Also, did you just have to search for the file name "monument" and the correct the capitalization and did that have to be done manually or were you able to just replace everything? Sorry for all the questions but my server was heavily damaged by 20w21a and I'm looking for any fix I can find.

@Gavin Pitt ... Your seed is corrupted. If you open your chat and type /seed, you will probably receive "[0]" as output. The same way, you can open your level.dat and add the seed to the locations it needs to be (If I am not forgetting any, there are two references on each of your dimensions). But deleting the chunks with the seed valid for the world will generate the same terrain.

Also, if you go anwhere you never generated, it will generate with different terrain.

This issue is caused by oppening your world on 20w20b.

@Gavin Pitt , please refer to the following post for a more complete solution.

https://www.reddit.com/r/Minecraft/comments/gttlj1/fixing_world_corruptions_from_last_snapshots/

Ok so fixing the seed then re-generating the chunks my witch farm is on will fix the mob spawning in the witch hut ? thankfully my guardian farm and spawns at the pillager outpost are still working.
Also, yes to confirm seed is stating 0, even though it is actually -45xxxxxxxxxxxxx
Thanks for the link to the fix 🙂

My seed wan't stated as 0 so my world isn't corrupted but my guardian farm sill won't get any spawns. So what should I do?

@Nic Tapia ... there are two corruptions in place here. 20w20b may have corrupted your seed, 20w21a corrupted the farms. The link in my commment put together all the solutions but all of them involve third party tools. Your case is only the fix for the farms, not the seeds.

@Gavin Pit , yes, fixing your seed and regenerating the terrain will generate a fresh witch hut. Works for all of the chunks you may have generated with this terrain issue as well. Also live an up on the solution, it's my post as well (:

I’m not sure if this helps anyone but this is what I did. So yes, I made a guardian farm and it no longer worked, but since I didn’t want to effect or change my world, I left all the files alone and did not use regenerating programs etc. Instead I went to find another ocean monument but in the new 20w22a snapshot. The ocean monument  I found was not in a place I have searched before and therefore the chunks I loaded were new for the snapshot. So, there were guardians spawning at this ocean monument. It will take a while to rebuild a farm, but I’m glad I was able to see guardians spawning at a monument. Again, I’m not sure if this helps anyone, but I just wanted to say this for those who might want to know!

This is going to be fixed eventually correct? Or do I actually have to go through the complicated process that I'll probably mess up? I've spent months draining this monument and building the farm. I really don't want to lose all of that work because of a stupid bug

If you don't want to fiddle with your world files manually, you can of course always restore the world from a backup, which you should have because you're playing in the snapshots.