Clients invalidly handling their connection during the status phase will cause a SocketException to be thrown, which is handled by the ClientConnection#exceptionCaught method. This results in a clientbound/minecraft:disconnect packet with the message 'Internal Exception: (stringified error)'to be sent to the client. However, this packet doesn't exist in the status phase, so the server logs the following exception:

Error sending packet clientbound/minecraft:disconnect
io.netty.handler.codec.EncoderException: Sending unknown packet 'clientbound/minecraft:disconnect'

I would expect this exception to not be thrown as sending a disconnect packet with text during the status phase makes no sense, and the true error is with the client rather than the server.