This is based on MC-79813
When you use a /tellraw command or a book with JSON to let the player run a command containing "§", they will get disconnected and their client freezes.
Command
/tellraw @p {"text":"Click","clickEvent":{"action":"run_command","value":"\u00a7kTest"}}
Game Output
[16:36:09] [Server thread/INFO]: Marcono1234 lost connection: TextComponent{text='Illegal characters in chat', siblings=[], style=Style{hasParent=false, color=null, bold=null, italic=null, underlined=null, obfuscated=null, clickEvent=null, hoverEvent=null, insertion=null}}
[16:36:09] [Server thread/INFO]: Marcono1234 left the game
[16:36:09] [Server thread/INFO]: Stopping singleplayer server as player logged out
[16:36:09] [Server thread/WARN]: handleDisconnection() called twice
[16:36:09] [Server thread/INFO]: Stopping server
[16:36:09] [Server thread/INFO]: Saving players
[16:36:09] [Server thread/INFO]: Saving worlds
[16:36:09] [Server thread/INFO]: Saving chunks for level 'Test test'/Overworld
[16:36:09] [Server thread/INFO]: Saving chunks for level 'Test test'/Nether
[16:36:09] [Server thread/INFO]: Saving chunks for level 'Test test'/The End
Note: The freezing might be caused by MC-92255, however the handleDisconnection() called twice warning is unusual
