From previous work by others (silentwisperer, et. al.) there are only 25 locations in an ocean monument that can spawn guardians. Guardians are supposed to require water to spawn. As shown in the attached *.mcworld file, guardians will spawn on solid blocks at these locations with no water present.

Expected: Guardians should not spawn without the presence of water.

Bug: Guardians spawn on solid blocks in air.

Notes:

1. The attached world is from silentwisperer's guardian farm video https://www.youtube.com/watch?v=14j8YH7YGNY
2. Guardians are spawning on both prismarine and acacia wood, i.e. the buggy spawning does not require temple blocks.