Possibly relates to MC-253055, as that's a similar issue, but with resource packs' sounds.json.

If you have multiple data packs loaded, and a tag is missing a reference, eg non-existing function, it'll print that it is missing that reference once for each loaded data pack.

Eg, having 2 data packs loaded, with the first pack (from bottom) having the error results in:

[15:01:28] [ServerMain/ERROR]: Couldn't load tag luigis_mansion:items/poltergust_3000/music_cannot_overwrite as it is missing following references:
luigis_mansion:items/poltergust_3000/music_cannot_overwrite/cathcing_chauncey (from Luigi's Mansion),
luigis_mansion:items/poltergust_3000/music_cannot_overwrite/cathcing_chauncey (from Luigi's Mansion)

Whereas having only the one with the error loaded results in:

[15:01:28] [ServerMain/ERROR]: Couldn't load tag luigis_mansion:items/poltergust_3000/music_cannot_overwrite as it is missing following references:
luigis_mansion:items/poltergust_3000/music_cannot_overwrite/cathcing_chauncey (from Luigi's Mansion)

Note, that in my test, none of the higher packs actually provide that tag.

Steps to reproduce:

• Make a valid data pack
• Add a tag to 1 data pack with an invalid reference (eg create data/minecraft/tags/functions/test_tag.json with the value

  {"values": [ "minecraft:non_existing_function"]}

  )

• Load the world
• Observe error in log listing the missing reference once
• Make another valid data pack/
• Use /reload
• Observe error in log listing the missing reference twice