Mine does the same at times. Sony TV and Sony rec/Amp along with a ROKU ultra. I haven't had time to troubleshoot yet but I'm thinking because of the HDMI settings on ARC and with telling the ROKU and TV and the Amp to turn each other on that there is simply a conflict.
I hope this at least gets you thinking in the right vein.
On occasion I have had my Samsung TV power on in the middle of the night. My guess is it's happening when either my Roku or my Shield get's an OS update and reboots. The device is sending a CEC power up command, which turns the TV and the AVR on. It's random, so tough to tell exactly what unit is causing it.
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