It happens for us with Webex app, no idea on the fix but i did just open a support case

Yeah I think that that may be my next step too.
It doesn't happen to every student just a couple. But to the point where they are missing assignments because of it.

Well in my case it is an issue with that specific app and JAMF has a case open with Apple, so it is a known issue

I think I found out what the problem was with ours. I had a similar issue where google chrome wouldn't install from the self-service portal, tried sending blank pushes, inventory refreshes, deleted from JSS and re-enrolled, restored etc.

Turns out the problem was with the restrictions I had set in a general profile. I wasn't allowing apps with a rating of 12+ and above. Chrome is rated 17+, so it would "install", and JSS would report is as being installed, but it wouldn't show up on the ipad itself. After removing the rating limit the app showed up just fine.

This behavior also happens when the app record in the catalog lists an outdated app version from the volume App Store. If you don't have apps set to automatically update, then you'll need to be aware of what app version is listed in the JSS. Self Service checks the JSS catalog, not the App Store for license info, and it won't install an old app version.

It's a pain, I constantly have to refresh the license for a specific app that wont push out.