I do not know why that would appear but try this...
Open the Settings from the Settings shortcut seen on the Home screen.
Scroll down to the bottom where to the apps category, then scroll way over to the right ad open the Special App Access
then open 'Energy Optimization' and then scroll down till you see the 'Device Health Services' and turn that Off
Home Screen > Settings > Special App Access > Energy Optimization > Device Health Services > Off
maybe after you have turned it off and checked results, then with it still set to off, unplug the power and then plug back in and go back in there and turn it back on.
Then check if the message still appears.