It depends on what option you selected when you added that app to the device or device group:
If you selected Latest (Auto Update) for app version, the individual ungrouped device or device group in question will automatically update to the latest version of the app in question without any manual intervention.
If you pinned a specific version of the app, the individual ungrouped device or device group will not automatically update to the new version. If you need the device(s) to update to the new version, you will need to follow the steps detailed here.
