Arduino uno - 4digit 7seg display via 74HC595 keeps blinking

Question

I am trying to get my 4 digit display (SH5461AS) count from 0 to 9 based on millis() function.

The problem is that it keeps blinking. Even if I display just one number, it shows then it goes black then it shows again, instead of staying on.. Also the upper segment (A) is somewhat delayed. Sometimes it shows, sometimes it does not. I am really not sure what is going on. It is best illustrated in the video: https://youtube.com/shorts/gmbNnvEYq2I

I have arduino UNO R3 hooked up to the 74HC595 8-bit register and from there to the corresponding 'data' pins on the display. It is a common cathode type so I have all of those connected via resistor to the ground.

I appologize for the messy cabeling:

From the display basically all resistors go to ground and all data cables to the register (Q0-DP omitted, segment A-Q7, B-Q6, .., G-Q1 [decimal number 1=A, 2=B, 3=AB,..]).

In the register I got VCC, Ground, data cables, EO grounded, serial data->arduino D4, storage clock -> D5, shift clock -> D6

 #include <LiquidCrystal.h>

//LCD
const int rs = 7, en = 8, d4 = 9, d5 = 10, d6 = 11, d7 = 12;
LiquidCrystal lcd(rs, en, d4, d5, d6, d7);

//7SEG DISPLAY
int LATCH = 5;
int CLOCK = 6;
int SERIALPIN = 4;

const byte numbers[] = {
  0b111111, 0b0000110, 0b1011011, 0b1001111, 0b1100110, 0b1101101, 0b1111101, 0b0000111, 0b1111111, 0b1101111
};

//OTHER

void setup() {
  //LCD
  lcd.begin(16, 2);
  lcd.print("Test!");

  //7SEG
  pinMode(SERIALPIN, OUTPUT);
  pinMode(CLOCK, OUTPUT);
  pinMode(LATCH, OUTPUT);

  //OTHER
  pinMode(13, OUTPUT); // turn off onboard diode
  Serial.begin(9600);
}

void loop() {
  countSeconds();
  delay(1000);
}

void countSeconds(){
    digitalWrite(LATCH, LOW);
    // int number = (millis()/1000%10);
    // Serial.println(number);
    shiftOut(SERIALPIN, CLOCK, LSBFIRST, numbers[0]); //for demonstration purposes display 0
    digitalWrite(LATCH, HIGH);
}

Any ideas what's wrong?

Answer 1

As @Mat pointed out, the reset pin on the shift register was not connected. I didn't realize I need to anchor it high. Solved all problems, I guess it was resetting unpredictably..