Why does Screen Time show wrong usage while iPhone is powered off?

When I have shut my phone completely down (usually around 9 to 3 due to high school) and I check my screen time at the end of the day, it usually says around 10 hours. I haven’t thought much of it until I checked when it was doing so much, and it said that I was doing “other” for the whole time it was powered off. It happens EVERY DAY (mon to fri). Is there a reason to this?

[Re-Titled by Moderator]