This is usually because either iOS Face/Touch ID has been disabled or because Strongbox convenience unlock has been disabled.
There are 2 locations (1 global and 1 specific to the database) for this setting in Strongbox. You’ll need to check both are toggled on. The 2 locations are:
- App Preferences (Gear icon in top right of home screen) > Advanced > Allow Face ID/Touch ID
- Database Preferences (Gear icon in bottom left of home screen) > Face ID/Touch ID Unlock
If that doesn’t help try restarting your device and making sure Face ID/Touch ID is otherwise working across iOS.