Well Kombo lad, i also know very little about it so i can't answer you.
all i know is that it did too in the original mod, i just removed every assets linked to the hammer

I know next to nothing about modding, so feel free to ignore my confusion, but how does throwing the grenades cause a crash when using Jacket's Piece? Other than that, it works like a dream

It's just a bug present in the original add-on that causes the game to crash when someone uses a throwable

i just removed the hammer, i dont know about that

Appears that it carries over the throwable crash bug from the parent add-on, unfortunately.