@SamsungAdam as I mentioned, It happens at random times. For example, I'm browsing on chrome and it happens suddenly; I switch to another app or go to home screen and the blinking does not go away until it randomly decidesto stop, be it minutes or seconds. It happened in the old phone that I returned and now on the new one that I ordered. Imagine yourself reading or watching something and your hand or anything else gets near the sensor and it turns the display off; do you call that normal? I really don't think so.
I did not test it in safe mode because it happens randomly. I don't want to stay on safe mode for a long time waiting for it to randomly happen, that's impractical, I get days without this problem and sometimes several times in one day day.
I wouldn't have purchased the second device, but I have invested a lot of money in accessories already so I ordered the new one hoping that it would be better, but it isn't at all.
Samsung's policy is ridiculous. They do not have replacement policy even if you receive your brand new phone faulty right out of the box. Your only option is to return it or send it for repair, and both options are time consuming and you will have to wait for a couple of weeks without a phone. You pay $1200 and this is what you get. Complete disappointment.
If you watch a video and even if proximity sensor is blinking, it shouldn't just turn off the screen. When I listen to a recorded audio message on whatsapp, the priximity sensor starts blinking, then message stops or I stop it, blinking stops. It is designer so that when you start listening to that recorded audio, main speakers on the phone are playing that message, so when you put your phone against your ear, then earpiece speaker starts to produce sound. It is made for privacy. I think similar happens when I listed to visual voice mail(I would have to double check that)
After reading all the response, a theory came to me:
As the proximity sensor is suppose to activate and blink during phone calls. Now, could a app, especially a spy app or malware be secretly turning on some call or audio recording systems in the phone and inadvertently activating the proximity sensor?
So is the blinking light a sign that something else is going on in the phone?