It seems that I run into a lot of the same issues as you do. Try seeing if you have the option to remove the app from that device in its device page. Then try going to Apps > Apps > search for the app in question (Apple Classroom). Open the page for it, and click on "Used" under the licenses section. This will show you a list of devices that have a license, search for the device in question, and revoke its license if it has one. Then try pushing it again. 

This is the direction I got on a ticket for a similar issue with Numbers a while back and it worked then, but I'm having the same problem with Pages on another device currently, and it's not even getting the license or letting me try to remove the app, so I'm not sure it will work. Worth a shot though!

Strange. It assigns licenses properly. And our settings make removing the app automatically revokes the license. I made sure to check before I added it and there were no licenses assigned before pushing the app.

Pushed the app, got the error (but with a functioning app), and a license is assigned. Remove the app, the license is also removed. Push the app again, installs without any errors and has a license assigned to it.

I also pushed Numbers to it and did not have any errors. Strange.

We are also seeing this duplicate request for xcode