New 8K 900R. When I press the on/off button on the remote to shut down—both the TV and the Spectrum box shut down, but the TV starts again with "HDMI 1, check device power, with a "Power-on" button.
The only other device I have is a DVD.
Maybe try holding down the remote for a little longer during the initial shut down to see if that helps. You can also try replacing the batteries to see if that helps.
Do you have anynet+ turned on? It can sometimes cause the tv to turn on if an external device is on.
Keep me updated!
The last question does this occur when the DVD player is unplugged from the TV?
This will be under the TV settings you can turn it off or on by going to Settings > General > External Device Manager > Anynet+ (HDMI-CEC).