iPhone 16 running iOS 18.1 Standby stops during the night

I put my iPhone 16 running iOS 18.1 on my MagSafe charging stand before bed and standby mode comes on as usual. 2 nights in a row now (lines up with iOS update) I go to tap my table to check the time and nothing happens. When I touch the screen it has changed to portrait mode even though the phone is still sitting in landscape. I can turn it to portrait mode then back to landscape and standby mode comes back on. This never happened before iOS 18.1. I also have charge limit set to 80% I wonder if it has something to do with it?

[Re-Titled by Moderator]