Check if there are any mods on your server that may add new liquids, eg RAGs framework. I have this issue on our server as well and it's the aviation fuel mod that's causing it, because it's not happening on a pure vanilla server.

In T164542#2302779, @Trashpanda69 wrote:

In T164542#2302777, @arthur_galvao wrote:

All the bodies when cutted only drop meat, bones and guts. The loot from the body disappear. As I mention above remove their clothes and gear first, if you chop them up with their clothes and gear still on them you’re despawning all of it.

Just following up on my earlier comment as have finally fixed the problem with the help of mod developer. After some testing I found the issue occurred after installing the first mod on the server which was the community framework mod (i.e. @CF), but if I wipe the server after installation, that fixes any issue with the grenades.

Same issue affecting a fresh server I've just setup, anyone find out what is causing this or how to fix it?