generated a gravestone as item that could be picked up; did neither disappear on breaking, nor release any items. All items lost.

same problem please lmk if u have found a solution

We have this issue too on our server, and with the henkelmax mod being updated to 1.20 we are considering to change mods, since they have a system to regain the items even in case a gravestone breaks or bugs out

Having the same problem in 1.20.1. Great Mod otherwise

It is not limited to drowning only if you die in water at all, it happens too. A solution that I would suggest is for the gravestone to be resistant to water.