No data delivered with `custom_notification`

`react-native@0.48.4`
`react-native-fcm@9.7.0`

Our app works fine with ordinary GCM notifications, but I wanted to use the `custom_notification` feature in order to run some logic on receiving background messages. However, when the app ‘wakes up’ on clicking either the library’s generated notification, or a manually created local notification via `FCM.presentLocalNotification()`, the notification that arrives through `FCM.getInitialNotification()` contains no data: only the flag `opened_from_drawer` and an empty `fcm: {}`. I’ve previously seen that when I had misconfigured the Android manifest and the intent matching the `click_action` was not associated with the main activity; but as mentioned above, it’s now working fine with regular GCM notifications.