Why does my screen look whitewashed?

Bought a secondhand iPod nano 5 and somehow it have a screen that displays whitewashed images. I thought it was because the battery has totally died and wasn't delivering enough power, so I took it apart and replaced it. However, after I replaced the battery and cleaned the screen press connector contacts, the screen still look white. The same problem occurred when I booted it with and without the casing. Here's the funny thing. I found no signs of water ingress, not deforming, no corrosion, nothing out of ordinary at all when I was replacing the battery. The motherboard is almost pristine with no signs of any damage. the screen is also as perfect as it can be. I tried resetting it using windows, Mac, even wiping the disk completely clean and reinstalling the system, nothing worked. The only improvement after a whole afternoon of cleaning and formatting is that the display returns to normal randomly but flashes white after a period of time.

here's a nano 4 for comparison.

I'm at a total loss right now. Is this a software issue or a hardware one? Does anyone have the same problem or have any idea what's going on?