There is a thread about this but posting stops around 2020 without any resolution to the problem. I have two Samsung tvs, a QN82Q6DR and an older plasma PN63B590T6FXZA. The 82" has the same problem of turning on by itself.
I have two problems. Both are using Xfinity with two remotes. First problem is either remote can turn on/off either tv. Second problem: the plasma which is in our bedroom turns on by itself every night at around 3:30am. Weird. The only reason I can think of is that my neighbor whose house/tv is pretty close to our house and has Xfinity cable also turns on their tv at this time. And this turns on our bedroom tv too! What to do?
The tv did not turn on at 3:30am after changing the update time from 2-4am to 12-2am. Did this solve the problem? If this is the problem it should turn on on the new time from 12 to 2am but it didn't.
I also changed the Anynet HDMI/CEC button from On to Off and then power off the tv for a minute.