If you use the driver app on an iPhone not updated to iOS 11 or above, notifications about new trip requests may occasionally not display correctly.
To fix this, open your phone's Settings app and head to Notifications > Uber Driver App. Switch your notification style from Banner to Alert.
After making this change, you should receive trip requests as pop-up notifications.
Also, please make sure to update the Uber Driver app to the latest version of iOS 11 or later available in App Store for iOS users.