Using a simple string with a custom namespace in a sound event resources location will fail, which causes the data pack to be considered invalid and not loaded.

This is a inconsistency with all others resources location parsing that accept custom namespace in the string format. The sound event resources location are the only one that require a specifique form to use custom namespace.

Know place when this inconsistency occurs: "ambient_sound" in biomes files, "sound_event" in jukebox_song files.

Know place when this inconsistency not occurs (you can use custom namespace in the string format): "playsound" command.

For example:

Note: I will use the "jukebox_song" file, but this inconsistency occurs in several others place inside the default data.

The default "sound_event" for the music disc "creator.json":

{
  "comparator_output": 12,
  "description": {
    "translate": "jukebox_song.minecraft.creator"
  },
  "length_in_seconds": 176.0,
  "sound_event": "minecraft:music_disc.creator"
}

However, if you want to use a custom namespace sound event, this doesn't work:

{
  "comparator_output": 12,
  "description": "Test custom: anubis",
  "length_in_seconds": 156.0,
  "sound_event": "custom:music_disc.anubis"
}

And you need to obligatory use this "complete" form:

{
  "comparator_output": 12,
  "description": "Test custom: anubis",
  "length_in_seconds": 156.0,
  "sound_event": {
    "sound_id": "custom:music_disc.anubis"
  }
}

To reproduce:

1. Download 'sound_event_bug-resources.zip' and place it in the resource packs folder. Add the resource pack to the active packs list.
2. Download 'sound_event_bug-data.zip' and place it in the world folder.
3. Attempt to load the world the data pack was added to.

What will happen:

The world will be prevented from loading by an error in the data pack.

What was expected to happen:

The world would load and a sound event with custom namespace can be used with his string format.