I have attached a 3x4 keypad to my Arduino Leonardo as an input method. Whenever I press the buttons, the majority of the keys work but specific ones don't. Here's my code, I've set it up to beep a piezo buzzer when it gets a keypress.

#include <Keypad.h>

int buzzerPin = 0;
const byte ROWS = 4; //four rows
const byte COLS = 3; //three columns
char keys[ROWS][COLS] = {
    {'1','2','3'},
    {'4','5','6'},
    {'7','8','9'},
    {'*','0','#'}
};
byte rowPins[ROWS] = {12, 13, 8, 10}; //connect to the row pinouts of the keypad
byte colPins[COLS] = {11, 7, 9}; //connect to the column pinouts of the keypad

Keypad keypad = Keypad(makeKeymap(keys), rowPins, colPins, ROWS, COLS);

void setup(){
    Serial.begin(9600);
    pinMode(buzzerPin, OUTPUT); //Set buzzerPin as output
    keypad.addEventListener(keypadEvent); //Add an event listener for the KeyPad
}

void loop(){
    char key = keypad.getKey();
}

void keypadEvent(KeypadEvent eKey) {
        // When the KeyPad will be pressed, the results will appear on the serial monitor.
        switch (keypad.getState()) {
        case PRESSED:
                Serial.print("Enter: ");
                Serial.println(eKey);
                beep(10);
                delay(10);
                break;
        }
}

void beep(unsigned char delayms) { //creating function
    tone(buzzerPin, 2000); //Setting pin to high
    delay(delayms); //Delaying
    noTone(buzzerPin); //Setting pin to LOW
    delay(delayms); //Delaying
}

I based my rows/columns off of this pin-out: https://www.jaycar.com.au/12-key-numeric-keypad/p/SP0770, but I later found out some of the columns had to be swapped :P

Here's a diagram of what's happening:

The keys in red do not work.

I wouldn't have posted this on stack exchange but it looks like an oddly specific pattern, and no matter what I changed, it didn't work.

(And yes, that is the exact keypad I bought from Jaycar)