I'm on a 1.20.1 modpack "Sanctum Network" and just as the title says the mobmasher just crashes the server whenever hitting an entity.

crash-2023-11-12_12.25.41-server.txt

looks like the mod Simple Enchantments is not handling fake players correctly.
It appears to be a MCreator based mod, and is firing off slash commands to do things, and is trying to do it in the context of MGU's fake player.