I've encountered this bug while I was trying to lower the spawn rates of my world by a ton, but for some reason nothing changes. I was able to figure it out by reading through the loot modifier mods and saw that it was True Music. Since I only planned on fixing it for I and my friend's server. I thought about sharing it instead.

P.S. it was a typo on the author's loot distribution files which completely broke the system reading it.

Here's my override fix https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=2829426015