Hi, so I just made a guardian farm by gnembon. It is his updated 1.12 farm. I am playing on my friends server running 1.13 with MCProHosting. Me and my other friend built the farm (drained and cleared monument) to realize that we got no spawns. We then lit up all caves in 128x128 area. We were still getting little to nothing spawns! It seems as though we would only get spawn when at least two players were in the killing chamber. If only one person was online there would be no spawns. Our render distance is set to 12 and I have looked up and seen that many people have used this farm on servers WITHOUT lighting the caves and already gotten an insane amount of drops (ft. Mumbo). Me and my friend are extremely disappointed as we have been working on this for weeks. I would like as much help as possible on this issue, thank you!
On a server your client render distance doesn't matter. The server needs to have render distance set to 10 or more to avoid the mob spawn bug.
For what it's worth, my guardian farm is still cranking out the evil fish. I just put my SSP world on my SMP server to test if it was some kind of bug with servers, and it still worked as expected. That was in 1.13.1 with the Mojang server (but I had previously tested in 1.13 with the same results).
You might want to contact the server host to see if there's anything they're doing that could affect your farm.
Was the server upgraded from 1.12 to 1.13 with the world still active? Did you dismantle the monument before the upgrade? I know that there was a bug during the snapshots that caused some monuments that had been destroyed in the older version to not be valid monuments in the upgrade.
This monument was entirely cleared and drained in 1.13. Was covered in kelp and seagrass when we found it. This was after we upgraded to 1.13. Also, sometime guardians will spawn, but I will only reach a max of 4-6 guardians at a time. ):