I just built a Project a while ago using a fast network and a Tablet. The loading of the Project was S L O W. I just tried a minute ago and the build was IMPOSSIBLE. I closed the browser, opened the browser again and went back to App Inventor and successfully built, albeit slowly.
Sorry your students are having issues too.
Something has happened since the weekend
- In many places, online learning has started (replacing classroom learning), stressing the Internet
- while your IT department indicates the problem is not on the school network end, there is a problem at the MIT end ... developer congestion. MIT does what it can. You might try the alternative server at http://code.appinventor.mit.edu/ . Have you tried that? Sometimes the code... server's load is less than the main server. If you use it, students will have to load their current Project aia file on the code server.
- Are your Kindle's using the latest Companion? Your students should be using Companion 2.60 . Having the latest Companion might make a difference.