I’ve removed the StackMob plugin because I want to see how the server performs with 1.13.2. Hopefully, we will not need to re-install the plugin, however we won’t know anything until we can monitor server performance with lots of players online.
Unfortunately, removing this plugin means that the server no longer recognizes stacks as multiple mobs. It will instead treat each stacked mob as just one mob with a custom name. I understand this is frustrating – if this causes you to lose anything important we will spawn it back in. If you’ve just lost a few cows/chickens/etc, though, I ask that you just breed them.