here is a video showcasing the bug
and yes it occurs consistently.
This occurs with all composite models that use the item/generated mesh
I ran into this issue while making this resource pack
was able to fix it by making a pseudo-mesh that has 256 cubes
https://modrinth.com/resourcepack/flaming-fire-aspect
yeah it turns out this was a bug with the mod "Item Regex". It has since been fixed on the developer's end lol