Guardians not spawning at Ocean Monuments

Did you open your world in any snapshot or pre-release prior to 1.16-pre1?

I opened in several snapshots with the same effect. anything before 20w14 opens in a tiaga biome instead of the ocean at the monument.

Guardians do spawn in new worlds that I create.

Can you provide the seed?

7133441834025945918. The monument I have cleaned out is near 2195, ,-1474. There are other monuments nearby that I also have cleaned out, but I have visited new monuments that only have elder guardinans. I'm sure I just missed something in one of the snapshots, but I do not know how to get it back

If I reload the same seed, I find the monument and there are guardians. I don't know why they don't show up on  my survival world.

Have you ever used any kind of mods or third party tools while playing on the world?

Never any mods. Purely vanilla.

OK, I may be on to something. When I put my level.dat file into chunkbase to get the seed number (I have done this before with this seed and it works) then it says 'Unable to get seed from file'. Could that cause my problem? It would explain why I get a different biome when I open in past versions.

As always, early development versions can cause corruptions like the one you are describing, so I recommend reverting to a backup of the world where this was not an issue, Your issue is a combination of MC-186087 and MC-186096, neither of which are going to be Fixed.