Classroom Sign In pages rely on the browser’s “LocalStorage” system, the same way that individual remembered sign-ins do. (If you are using the mobile app, this information is stored as app data.)
If your browser does not allow websites to save data, the classroom sign-in page cannot be remembered. Common causes for this are school IT settings (such as wiping browser data every night), or using Private Browsing or Incognito mode in the browser. These settings affect only remembered sign-in information, and the rest of the program works as normal.