Can't join server - string length longer than max allowed

When I try to join my server I get this message:

[16:09:47] User Authenticator #1/INFO: UUID of player quadrplax is bb1be76b-def4-4b83-aba4-81eb0ddb8458
[16:09:47] [Server thread/INFO]: quadrplax[/

{removed}

:60420] logged in with entity id 265 at (155.5, 64.0, 253.5)
[16:09:47] [Server thread/INFO]: quadrplax joined the game
[16:09:48] [Server thread/INFO]: quadrplax lost connection: TranslatableComponent{key='disconnect.genericReason', args=[Internal Exception: io.netty.handler.codec.DecoderException: The received string length is longer than maximum allowed (12 > 7)], siblings=[], style=Style{hasParent=false, color=null, bold=null, italic=null, underlined=null, obfuscated=null, clickEvent=null, hoverEvent=null, insertion=null}}
[16:09:48] [Server thread/INFO]: quadrplax left the game