In 1.17-pre1, item predicates and block predicates were changed from only accepting a single ID to an array of IDs. Fluid predicates however were left unchanged, leading to extremely inconsistent behavior. Apart from fluid predicates not having an "nbt" property, they were exactly consistent with block predicates.

Example predicate showcasing the inconsistency.

{
  "condition": "minecraft:location_check",
  "predicate": {
    "block": {
      "blocks": [
        "minecraft:water_cauldron",
        "minecraft:lava_cauldron"
      ],
      "state": {
        "level": 1
      }
    },
    "fluid": {
      "fluid": "minecraft:water",
      "state": {
        "level": 1
      }
    }
  }
}