It sounds like you are running into CEC issues.
If you are running all of your equipment into the A/V receiver, then on to the TV, then you don't need HDMI CEC turned on. Just turn on the receiver and turn on the TV separately. Oh, and this is a good example of why universal remotes are the bomb.
But, when HDMI-CEC is turned on, strange things can happen. Especially if you have some device off to the side which may be going to sleep or doing something else. Perhaps a streaming device like a Roku or AppleTV. It may wake up with your 'ON' command, but when it goes to sleep, it shuts EVERYTHING it can down. Hey! That's EXACTLY what CEC is supposed to do. Except, then you understand why CEC sucks.
Turn off HDMI-CEC on everything you can, and see if you fix the issue. If you have any other devices beyond your cable box, Denon, and Samsung all connected, then also turn off HDMI-CEC in those devices.