Cannot setup Public App's device assignment (iOS)

[HKCA]

We want to install (remotely) a public Apps to some of our devices (iOS). Firstly we have created an "Assignment Group" for these devices. Then, we go to Resources -> Apps -> Public to search and add the App, then we set the assignment group for the App and save the settings. However, when we go to the App -> Devices page, there is no device assigned (showing "No Records Found") for the App. The above steps works before, but today it is not working. I have repeat the steps many times but with no success. Could someone please help? Thank you so much.

[EricPlent]

Is the app assigned to an OG higher than where the device smart group was created? For example, in my system I add all applications at the top level and create assignment groups at lower levels (where devices are enrolled) as needed for specific use cases. This way, the assignment group will appear as an option when assigning the app regardless of where it exists in the lower OGs. 

[AlexanderMuc]

If you want to install iOS apps remotely, you should use Purchased Apps, not Public Apps.
Purchased Apps are used to buy app licenses via Apple VPP and assign them to the devices. WS1-UEM can then install these apps directly on the devices.
Public apps should only be links in the AirWatch Catalog that users with personal accounts can install.

I know the behavior described by you from Android Public Apps, if someone has only specified the URL of the apps from the Play Store when adding the Android app. Then the app is not managed by Managed Google Play and is the iOS equivalent of "Public" to "Purchased" apps.