While the Update Aquatic brings a lot of great new features to the game, it has broken quite a bit of older mod capability. This is primarily because there were some major re-writes to the way it generates the world. These re-writes do improve the game play quite a bit, but it means that nearly all of the plugins in use on this server are completely incompatible with 1.13.
Until those plugins get updated (some may never), the server will remain a 1.12 server. I’ll post updates here as more information becomes available.