Apple App Store and Automatic Updates

FileWave can request updates for managed App Store apps when a newer version is available. For admins, this usually shows up as an app that keeps reinstalling or updating after device check-in, even when the assignment has not changed.
How does FileWave detect if there is an update?
For iOS 11.3 and later, and macOS 10.13.4 and later:
Apple's MDM protocol returns update information when FileWave requests the installed application list. Each App Store app can report the HasUpdateAvailable flag. When that flag is true, FileWave can send the device an InstallApplication command to update the app.
For previous OS versions:
Every hour, FileWave contacts Apple's iTunes database and updates metadata for applications used in your environment. When a device checks in for Verify, FileWave compares the application version reported by the device with the version from iTunes. If the iTunes version is higher, FileWave treats the app as update-eligible.
The automatic update process does not work as expected, what could be the reasons?
If the flag is not provided by the device (older iOS / macOS version for instance), it may happen that the version from iTunes and the version reported by the device are not accurate (they are filled by hand by the developer and they may be incorrect). Apple introduced the hasUpdateAvailable flag exactly to solve this problem.
From Apple's documentation:
If 
true, the app has an update available. This key is present only for App Store apps. In macOS, this key is present only for Volume Purchase Program (VPP) apps. This status updates daily and isn’t always up-to-date when installing an app.
The flag provided by the device is not always reliable. FileWave only requests an app update once a day. The InstallApplication command is not sent again on the same day when the device reports 
HasUpdateAvailable=True and FileWave has already sent that command. If the device still reports the flag the next day, FileWave will request the update again.
Some iOS versions have reported this flag incorrectly even after the application is already up to date. If the flag does not update within 24 hours, FileWave may request the app update again each day, which can affect users and network bandwidth. In this situation, contact FileWave Support and AppleCare so the required FileWave and device logs can be collected. Updating iOS or macOS to the latest available version often resolves the device-side reporting problem.
In FileWave Client Info for impacted devices, check the Managed Applications tab. If the flag is always "True" after the app is already current, the issue is likely at the device or Apple MDM reporting level rather than the FileWave assignment.