why does my screen-time show 7 hours was spent using the system, even thought I was sleeping?

So I just woke up and checked my iPhone to see that I somehow have about 7 hours spent using the app called “system”. I am pretty sure that I was sleeping through the entire night, so I couldn’t have used my phone at all. I haven’t been on any sketchy websites. Before I slept, the only major change I made in the iPhone was adding limits like 1 hour of YouTube and the rest of the apps 6 hours.