Have you also tried using the Low Power Mode setting? See the last paragraph in:
As to the issue you are referring to, I suspect (but just a guess) that it might have something to do with the "Use Background App Refresh" section in:
where it says: After you switch to a different app, some apps run for a short period of time before they're set to a suspended state. Perhaps that "short period of time" is what's showing up in your screenshot. Again, just a guess.