iOS Contacts App & vCard Contacts
In order for vCard contacts to be visible in your local iOS Contacts app, an iOS configuration profile will need to be installed on your device. This iOS configuration profile simply allows your iOS device to connect to vCard's servers to retrieve your vCard contacts and display them in your iOS Contacts app. Do note that you may not modify your vCard contacts from the iOS Contacts app. At no time will your local device's contacts list be sent to vCard's servers as this access is completely controlled and managed by your iOS Contacts app.
Reinstalling vCard App & iOS Configuration Profile
Due to an iOS bug, you may need to remove vCard's iOS configuration profile when you use the same vCard ID with the vCard App and reinstalls the iOS configuration profile. Installing the iOS configuration profile again with the same vCard credentials triggers the iOS bug where the vCard contacts no longer show up in the iOS Contacts App. Removing the profile and re-installing the CardDAV configuration profile solves the problem.