My app lose auth state *NEED HELP ASAP*

[MimiBoo]

I have an app that uses real-time database and phone auth, and I use:
FirebaseAuth.instance.currentUser
to get the current logged user to show either home screen or login screen and after i don't use the app in a while and open the app It show me home screen as if I'm logged in but can't access database unless i Signout and relogin.
but before doing that when i use
FirebaseAuth.instance.currentUser.uid
It prints my uid, I've had this problem with this app for almost 3 months I have another app that uses the same code for login and register and it works fine