I recently gave my Procolor to friend trying to quit smoking. I used it for about 3 months intermittently, but I don't believe it has a stealth mode.
I know you can turn the LEDs off, but I never saw where you could turn the screen off. I never really looked for a stealth mode with it, but don't recall every seeing one either. If it were in stealth mode, I'm guessing the LEDs around the screen would also be off, not just the screen. I know you can set the LEDs to be always on, always off, screen on, and vape on I believe. This doesn't affect the main display though.
I hope someone responds here with some good news for you. I'm wondering if the screen on your mod is toast. It's possible there's a button combination for stealth mode, but I can't seem to find one when googling for it.
Good luck