I'm using Firebase auth, and haven't done anything to change the default implementation.
When I quit my app on an iPhone and restart it, I'm logged out. This is unlike any other app I use (Instagram, Chrome, Spotify, etc). I should be able to restart the app (in case it crashes or I get stuck for some reason) and still be logged in. I'm still on the same phone, so there's no reason to log me out unless I explicitly ask to log out.