I face the same problem. It turns out the MicroSD card the problem. Do you have MicroSD card inserted? If yes, try pull it out for couple of days.

Mine now no restart at all after remove the microsd card

Don't install anything,  let it be stock and see happen again or not. If happening then you need to visit SC as probably the unit is something wrong.

So far I think nearly all users here never face auto reboot issue.

Hi,

I have the same problem with you before. When I got the new Note 4 in less than 3 hours it already randomly restarted. At first, I thought I was accidentally pressed the power button so never bother about it.  But when I put it on my table after not using it for a while it will auto restart say after 10, 20 or 30 minutes. I have not installed any Apps yet, not even signed in to my Google Account or Samsung Account, etc.

The auto restart began even no SIM card inside. Initially, I thought it could be no SIM card inside. Therefore, I put in the SIM card but after a short while it will still auto restarted. At that time I have not used any memory card.

The next day I called the Samsung Service Center by complaining to them I got the new Note 4 in less than 1 day already have this auto restart issue. Why the quality control is so lousy?? Since it was less than 1 day they asked me to go back to place of purchase to ask for 1-to-1 exchange. When I went to the seller they asked me to go to Samsung Service Center for warranty claim. It is very sad isn't it they just pushed me here and there. But after I explained the problem to the seller, I was lucky that the seller replaced another new unit of Note 4 for me, Since then, I never have any auto restart issue in my Note 4.

This is definitely is the phone's hardware failure, they have to replace a new unit rather just repair.

I am writing this to you because I know how you feel now! I was having the same situation like you. If can, ask them for a new unit. This is not the software problem.

Good luck!!