You are right that uSD card is optional and not required. Without the uSD card, the LCD should still go past the ‘Detecting uSD card’ screen in less than 10 seconds. I am wondering if the uSD card slot has an issue or perhaps has a reflow problem. If you can, could you use a magnifying glass and check the solder joints on the uSD card slot, and see if there is any potential solder bridge or unsolder pin?