Motor encoders randomly start counting backward, then go back to normal

I am making an Arduino-controlled differential drive robot, and I am having the following problems:

• the encoders built into the motors are being used for measuring the rotary displacement, and while running they will randomly start counting the opposite direction of their rotation for a second then start counting the right direction again

• What can I do in terms of differential and integral control that will lead to a consistent turn every time?

MY CODE:

'#'include <DueTimer.h>

'#'define MOT1 5 //right motor speed pin (PWM)

'#'define MOT2 6 //left motor speed pin (PWM)

'#'define DIR1 4 //right motor direction pin

'#'define DIR2 7 //left motor direction pin

'#'define EN1A 10 //right motor encoder phase A pin

'#'define EN1B 11 //right motor encoder phase B pin

'#'define EN2A 8 //left motor encoder phase A pin

'#'define EN2B 9 //left motor encoder phase B pin

volatile long right_enc = 0;

volatile long left_enc = 0;

volatile long left_enc1 = 0;

volatile long left_enc_diff = 0;

void setup() {

  // put your setup code here, to run once:
 //set pin mode, attach external interrupts to encoders with ISR vector, set initial direction and speed of motors.

  pinMode(MOT1, OUTPUT); // Set ENC1 as output

  pinMode(DIR1, OUTPUT); // Set DIR1 as output

  pinMode(MOT2, OUTPUT); // Set ENC2 as output

  pinMode(DIR2, OUTPUT); // Set DIR2 as output

  attachInterrupt(digitalPinToInterrupt(EN1A), countRight, CHANGE);

  attachInterrupt(digitalPinToInterrupt(EN2A), countLeft, CHANGE);

  digitalWrite(DIR1, HIGH);

  digitalWrite(DIR2, LOW);

  Serial.begin(9600);

}

void loop() {
  // put your main code here, to run repeatedly:

left_enc = 0;

//left_enc1 = left_enc;

while (-left_enc < 1023){

analogWrite(MOT2, 100);

analogWrite(MOT1, 50);

Serial.println("left_enc: ");

Serial.print(-right_enc);

Serial.println(" ");

Serial.print(" ");

}

analogWrite(MOT2, 0);

analogWrite(MOT1, 0);

for (;;) {
   // statement block
}

}

void countRight(){

  if (digitalRead(EN1A)){

    if (digitalRead(EN1B)){right_enc++;}

    else if (!digitalRead(EN1B)) {right_enc--;}

  }
}

void countLeft(){

  if (digitalRead(EN2A)){

    if (digitalRead(EN2B)){left_enc++;}

    else if (!digitalRead(EN2B)) {left_enc--;}

  }
}

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