Modifier Switch

It must be some bug. I swapped the ON/OFF switch for an ON/ON and solved with

int togglePin1 = 9;  
int togglePin2 = 10;
  if (digitalRead(togglePin1) == HIGH) {
    char key = keyp1.getKey();
    if (key != NO_KEY) {
      Serial.println(key);
      Keyboard.press(key);
      delay(150);
      Keyboard.release(key);
    }
  }
  if (digitalRead(togglePin2) == HIGH) {
    char key = keyp2.getKey();
    if (key != NO_KEY) {
      Serial.println(key);
      Keyboard.press(key);
      delay(150);
      Keyboard.release(key);
    }
  }

Any of the other solutions would result in the same issue.

It must be some bug.

In the hardware, if changing the hardware corrected the problem.

did you try :

  if (digitalRead(togglePin1) == HIGH) {
    char key = keyp1.getKey();
    if (key != NO_KEY) {
      Serial.println(key);
      Keyboard.press(key);
      delay(150);
      Keyboard.release(key);
    }
  }
  else {
    char key = keyp2.getKey();
    if (key != NO_KEY) {
      Serial.println(key);
      Keyboard.press(key);
      delay(150);
      Keyboard.release(key);
    }
  }