Throwing item into Ectoplasm (the blue liquid) causes crash/freeze with Itemphysic installed. In multiplayer there seems to be a good chance that the backup won't work and world will crash on load.
No other mods, logs don't have any information

(link to itemphysic mod version used)
https://modrinth.com/mod/itemphysic/version/HK8tjlkI

might have something to do with ectoplasm dealing freezing damage?

try turning off ectoplasm freezing damage in the netherexp-common.toml file and see if it fixes anything

Turning off ectoplasm freezing damage didn't work.

(the config didn't reset or anything after restarting, and the freezing damage was turned off so the config works)

I'm not a programmer but I think it's related to ItemPhysic's item entity buoyancy stuff. This guess is also what led to me finding that ItemPhysic was the cause of the freeze.