Android: My Contacts App syncs your contacts automatically. Please ensure that the sync option is enabled from your phone settings. But, if My Contacts App is killed while running in the background, the contacts will not sync. This mostly happens when you have cleaner Apps installed on your phone or when there is an extremely low memory situation.
iOS: The first sync needs to be performed manually from My Contacts App by pressing, “Sync now” button. Subsequently, iOS will continue to sync your contacts automatically even if the App is running in the background. But, if My Contacts App is killed while running in the background, the contacts will not sync. This happens when you have cleaner Apps installed on your phone or when there is an extremely low memory situation.