Unless I am misreading something, the Leech enchantment is causing our server to crash. It has occurred a few times now, and the server crashes always correspond to when someone with a Leech-enchanted sword was fighting. If needed, I can attach the other crash reports.

crash-2021-11-29_05.31.53-server.txt

I suspect this occurs when a non-player entity attacks something with status effects and the mod cant handle giving an non-player entity status effects from Leech,

Thanks for reporting this. In the next update (for 1.18.1) it will be fixed! :)