CrashFixer is a plugin that allows you to protect your server by vulnerabilities that cause your server to crash. The plugin is complete for some options.
Some special characters make the player by using it or by sparing them make your server lag this bug comes from mojang. #BlameMojang.
For the moment there is no solution so I suggest you use my plugin which easily detects these special characters. the configuration is configurable you can add other characters you know. there are configurable prevention messages and if you want to kick the player. this bug has appeared since the update 1.10.1 !