Head items randomly not stacking

[JorisvD01]

Versions
Plugin: 7.0
Paper version 1.21.11-132-ver/1.21.11@c5eb079

Describe the bug
We have heads setup as voting reward items using the SkullURL & Material: PLAYER_HEAD. However, some heads stack, but others don't. Heads of the same kind sometimes stack, but other times don't. This is seemingly random, as I can reproduce this when giving myself a lot of them right after eachother.

To Reproduce
Steps to reproduce the behavior:

1. Add a item with SkullURL as reward; For example what we are using;

  4021:
    Items:
      item1:
        Material: PLAYER_HEAD
        SkullURL: http://textures.minecraft.net/texture/282fd4afb3d4c81ab8863fcb9409d1b2b35d1f6684f9a2f515c4eae9f2ee3e2f
        Name: '&2Pot Augurken'
        Lore:
          - '&8Vote beloning'
    Messages:
      Player: '&6&l[C&b&lV]&7&l・&aVotes&7 | &7Je hebt een &2&lPot Augurken &7ontvangen!'
    Sound:
      Enabled: true
      Sound: 'entity.player.levelup'
      Volume: 1.0
      Pitch: 1.0

2. Give your self this reward item multiple times, sometimes it stacks, sometimes it won't

Expected behavior
Items are the same kind, thus are allowed to be stacked

Screenshots/Configs

Additional context
Let me know if you need other context, or the full rewards file

[BenCodez]

Not sure what I'll be able to do about it. Does it happen on other skulls when not using a url?

[JorisvD01]

Haven't tried that, but I assume it doesn't. I checked, and it seems the item ID data is the only difference. Are the skulls data cached? Maybe that could be an option?

[BenCodez]

Can you try anything other than url and see what happens? I think it should already cache, but I'd have to double check that.

# Skull options
# Use material PLAYER_HEAD and %player% for player skulls
#Skull: 'PLAYERNAME'
# One place to find skull textures is here: https://minecraft-heads.com/
#SkullTexture: 'SKULLTEXTURE'
#SkullURL: 'URL'
#Get texture from a player uuid
#SkullUUID: 'PLAYER UUID'