Sorry to hear you are having these problems guys
My note 4 which i have been using for about 3 weeks now, had 4 random restarts, 3 while looking at photos in Gallery and 1 restart when i was trying to open a game. I do not remember how many apps I had opened when these restarts happened.
When no apps in Recent, my RAM is 1.4 - 1.5 (this is what is shown in Settings -> App Manager). However, when all apps closed, when you go to Recent and then Active app, Ram status is 1.7 of 2.72 available? Shouldn't those 2 figures be the same?
Also, would the phone possibly restart if it's running out of RAM?