The lower and higher nibble are swapped on the display pins...
That's why a statement such as this is used. You have to use your pin numbers, in the proper order, inside the parentheses.
myLCD LiquidCrystal_I2C ( 0x20, 4, 5, 6, 0, 1, 2, 3, 7, POSITIVE );
This would be easier to do if there were appropriate comments preceding and following the statement.
//LiquidCrystal lcd(RS, E, D4, D5, D6, D7);
LiquidCrystal lcd(7, 8, 9, 10, 11, 12); // put your pin numbers here
Don
Edit: I hope they both have fixed their backlight circuits by now.