In fact, since It can't be reproduced in vanilla, It is probably the data pack.
One, and It makes certain mobs drop skulls, (That might be the issue) Anyway, I did decide to switch back to a 1.13 backup though. Sorry for taking a while with a reply
It happens with every Animal I've killed with this stone sword, (pigs, chickens, cod) I don't know why though
Also Happens with cows too.
Yeah, I just checked the duplicate issue, and he used the same data pack, sorry for wasting your time with this.