These are the reasons I had to drop the plugin in its current compiled state.
The first, I dunno if it's intended to be like this; in any case it's tolerable.
I started a test game with someone on the latest spigot build, our arena is on another world than the regular one. After two rounds it picked up someone else in the server and "destroyed" (multiworld inventories being used) that person's inventory.
Finally, /hga and /hg show a bunch of 'nulls'.