Unplug the TV for 30 seconds.
Try to update the software.
Disable the Power On with Mobile option.
This type of issue will need to be addressed by having the unit serviced. If the unit is in/out of warranty you can use the following link to find a list of service centers near you that can do the repair: http://www.samsung.com/us/support/service/location.
Jesus! What the heck is all this nonsense???
We bought an insanely expensive smart tv you have to unplug all devices from everytime you turn it off?
I dont have words, is this a stupid prank from Samsung, or what? 😂😂
It's cool that we(consumers) are diagnosing a problem THAT SAMSUNG should maybe look into it. I don't know about anything about business or anything about loyal customers. CLEARLY, the solutions that you are giving us isn't working. The real problem is that nothing is getting communicated to the engineers to actually help us fix this  problem. I can't believe we spent this much on a product and the tv can't even stay turned off. The basic functionality of a TV and Samsung has failed us.
Working solution: Put some black electrical tape on the front of the remote to block the IR transmitter from turning the TV on on its own.
As I've previously suggested, putting black tape on the remote's IR transmitter fixed it for me. I've had it for quite some time now and the TV doesn't turn on by itself anymore. The TV can still be controlled no problem since the remote is also paired on Bluetooth.
I have a Samsung 82" 82RU8000WXXY recently bought (2 weeks ago). Noticed the same problem where the TV randomly turns on a few seconds after turning off. It doesn't happen everytime but does happen every now and then. It's so new that I don't have anything connected to it (no HDMI connections, Soundbar, No Antenna, Nothing). It's only got Wifi connected and we have only used streaming apps (Netflix, Amazon)
It's obviously still in warranty and I also purchased extended warranty. I am worried and thinking what to do.... Obviously spent alot of money for the big screen and went with a big named brand so I don't have to face these crappy issues... Wasn't prepared for this.
Samsung doesn't really care. A technician just left my residence for the 3rd time attempting to fix the problem. The inconvenience of having someone in my home for a 3rd time is not what I expected from Samsung who should replace an obviously defective tv. Not happy and will contact BBB if I need too, just to leave a negative review about Samsung. Once again I have to replace and download all that I had before they reset the tv for the 3rd time. I have 2 other Samsung tv's and I will spread the word and not purchase anymore Samsung products like I did with Sony many years ago. I'll give LG a try next.