You may face an issue where your teacher site has been reverted back to an old version. Precisely, the site has been changed to the old SLS1 version. You would like to know how to get your content back and stop this issue from happening again
The solution to this issue is to use the article Restore a Previous Version of a Page to restore the latest version of the website from history.
In case the same issue occurs again after applying this solution please open a support ticket and provide the URL of the website that was reverted back to the old version.