Hi! I’ve been having the same problem since the update too, as I regularly switch off completely mi iPhone every night. However, recently I found a way to bypass this glitch and it’s by having a widget. I’ll show it in screenshots, but when I check screen time on settings, it shows 11+ hours like you mentioned, like if I’d been all night using it, but when I check it on the widget, it shows the correct time usage. Hope this helps you until we get an update :)