My system.out.printf doesn't show before a scanner's nextLine method

Question

This is my display interface

public interface Display {


    /**
     * <p>
     * Defines how a display decorates each line</p>
     */
    public enum Decorator {
        /**
         * <p>
         * {@code ***}The default string shown around messages</p>
         */
        MESSAGE("***"),
        /**
         * <p>
         * {@code ?}The default string shown after a memory location to input an
         * instruction</p>
         */
        INSTRUCTION("?"),
        /**
         * <p>
         * {@code >>}The default string shown during the execution of a
         * simpletron program when requesting for input</p>
         */
        INPUT(">>"),
        /**
         * <p>
         * {@code }An empty string</p>
         */
        NONE("");
        private final String decorator;

        private Decorator(String decorator) {
            this.decorator = decorator;
        }

        @Override
        public String toString() {
            return decorator;
        }
    }

    /**
     * <p>
     * Display the welcome screen</p>
     */
    public void splashScreen();

    /**
     * <p>
     * Displays a message without formatting
     * </p>
     *
     * @param message The message to displayInline
     */
    default void show(String message) {
        format(message);
    }

    /**
     * <p>
     * Displays a message with formatting, works just like the
     * {@code String::format method}
     * </p>
     *
     * @param message The message to displayInline
     * @param args    The

     */
    public void format(String message, Object... args);

    public static class Messages {

        /**
         * <p>
         * The message that greets the user when they load simpletron</p>
         */
        public static final String WELCOME_MESSAGE = "Welcome to Simpletron!\n"
                + "Please enter your program one instruction\n"
                + "(or data word) at a time. I will display\n"
                + "the location number and a question mark (?)\n"
                + "You then type the word for that location.\n"
                + "Type -99999 to stop entering your program.";

        public static final String READ = "Enter an integer";
        public static final String HALT = "Simpletron execution terminated";

        public static final String DIVIDE_BY_ZERO = "Attempt to divide by zero";
        public static final String FATAL_ERROR = "Simpletron execution abnormally terminated";
    }
}

This is the concrete implementation

public class CommandlineDisplay implements Display {


    @Override
    public void splashScreen() {
        Arrays.stream(Messages.WELCOME_MESSAGE.split("\n")).forEach(line -> format("%s %-43s %s\n", Decorator.MESSAGE, line, Decorator.MESSAGE));
    }

    @Override
    public void format(String message, Object... args) {
        System.out.printf(message, args);
    }
}

This is the implementation for the system's input

public class CommandlineInput implements Input {

    private static final Scanner keyboard = new Scanner(System.in);

    @Override
    public String nextLine() {
        return keyboard.nextLine();
    }

}

And last but not least this is the main method

protected void runSystem() {

        display.splashScreen();
        int index = 0;
        int inputValue;
        int memorySize = memory.getSize();
        while (index < memorySize) {
            display.format("%2d %s ", index, Decorator.INSTRUCTION);
            inputValue = Integer.parseInt(input.nextLine());
            if (inputValue == -99999)
                break;
            if (inputValue > 9999 || inputValue < -9999)
                continue;

            memory.set(index++, inputValue);
        }
        displayMessage("Handling operations");
        while (CPU.Register.INSTRUCTION_COUNTER.getValue() < memorySize) {
            handleOperation(cpu.execute(memory));
            if (CPU.Register.OPERATION_CODE.getValue() < 40)
                CPU.Register.INSTRUCTION_COUNTER.setValue(CPU.Register.INSTRUCTION_COUNTER.getValue() + 1);
        }

}

The problem I am facing is the command line blocks for input without showing the message from display.format method call, I'm just frustrated I've done basically everything I can think of including changing the input implementation to buffered reader and running with maven, still the same problem