In 1.20.1, tipped bolts (of any kind) shot by a crossbow have a missing texture (tipped arrows have their proper texture though).

Additionally, diamond and netherite tipped bolts cannot be shot from a crossbow, as they are not in the spartanweaponry:bolts item tag (manually putting them in the item tag using a datapack fixed the issue for me).

Yeah, that was due to a renaming oversight. I forgot to change the name for the entity textures when I initially made version 3.0. It's been fixed now (and was already fixed in versions for MC 1.18.2 and 1.19.2)

Do you know what's causing the missing textures though?

Thanks for letting me know about this!
I've added both the Diamond and Netherite Tipped Bolts in the spartanweaponry:bolts tag, which will be in the next 1.20.1 update

The update with both fixes is now live!
Closing issue