When I created a server using the mob hunting plugin: https://www.spigotmc.org/resources/mobhunting.3582/. My server would crash every 5 to 10 minutes. I don't know If it is just me or not but it happens. When it crashes my server it doesn't save any progress anyone else does. Unless you do the command /save-all. Which only save inventories and world changes, but not achievments and mcmmo skill levels. I found this out after I removed the plugin from my server which then stopped the server from crashing every 5 to 10 minutes. So if this is a problem with either my server or the plugin, I don't know. Just wanted to throw this out.