Most sprites don't "update" when on GUI

[Csazker]

https://gyazo.com/be18c94d8d2fa1ce4f7396154d4bec39
First of all, I am on Fabric for 1.21.4 and 've already tried the resource pack alone.
As the title implies, most food-type items are only animated on my hand and not on the GUI, whereas others - i.e. most stews - are animated both on the player's hand aaaand on the GUI, so it may be some code thingie, or is Fabric not rendering custom item data properly?

From this GIF - which is part of the resource pack's description - I understand it's not supposed to be like this? 'Cause the sprites are correctly updated there.
Anyways, thank you in advance for giving us one of the best mod/resource packs out there.