Not Charging

Hello,

I have an iPhone 12 updated to the latest iOS version. For a few weeks now, when I plug in my phone at night, it appears to be charging but, when I wake up in the morning, it's at the same battery level than the before, or lower.

When I go to the Battery section in Settings, it shows that the phone was in fact plugged in and charging, but with a decreasing battery level.

When I plug it in during the day, it usually charges fine. Could this be related to the Optimized Battery Charging feature?

I'm hesitant to think so because in the morning the phone is not at a usable battery level that will get me through the day.

Thanks.