Sometimes when a player leaves the server or switches between bungee servers their items aren't yet synced properly.
This causes an issue where the player can store items in a chest, switch servers quickly and still have the items on the other server. If they then switch back to the other server after waiting for sync they have duplicated the items.
I have my sync-time in config set to 1 minute.
There's multiple ways to dupe the items, but they all have to do with switching servers.
Sometimes when a player leaves the server or switches between bungee servers their items aren't yet synced properly. This causes an issue where the player can store items in a chest, switch servers quickly and still have the items on the other server. If they then switch back to the other server after waiting for sync they have duplicated the items. I have my sync-time in config set to 1 minute. There's multiple ways to dupe the items, but they all have to do with switching servers.