Nowadays there are many issues Minecraft server owners have to fight. One of such issues are exploits and glitches in Minecraft server. It’s bad enough there are plenty of duplication glitches on Minecraft servers but there are also worse issues.
Recently more and more modded clients started packing features like crashers, those are usually simple ingame commands that would cause Minecraft client or Mod to send invalid or bad data to the server. As result the server would hang or even crash. In some cases the server could “kinda crash” to the point where it would be super lagy and players wouldn’t be able to join, but the actual server would not be offline.
To combat that various plugins started showing up, but there are actually just a few that work. One of such plugins so RoweFix and another even better is ExploitFixer. Generally running those plugins is a must because without them Minecraft server would accept any packages even if they’re invalid and would cause crash.
So beware. You can find ExploitFixer on SpigotMC forums or you can build the plugin yourself, source code is available on Github.