Moodle is not a place for storing course materials. The Moodle Support team periodically delete old courses to prevent the system to become overloaded and to avoid the multiplication of reused files.
At any given moment, only 5 terms at a time will be kept on the platform, from the current term up to and including the corresponding term from the previous year, including the summer sessions. Anything earlier will be deleted as soon as a new term is created.
TBD
We encourage you, when making major changes to your Moodle site, to do a backup, so you can then restore your course in the event of data loss, or when you need to upload the materials to a new course.
It is best practice to always have course materials saved and backed up outside of Moodle. You can use OneDrive or any other online storage tool (Google Drive, Dropbox, etc.) and easily link to your resources from within Moodle without necessarily uploading the files. This will save a lot of storage space in Moodle, and it will maintain fast access to the resources (big files tend to be slow when downloading).
it is also highly recommended to make a backup copy of ALL graded assignments uploaded on Moodle. It is not advised to simply store assignments in Moodle because those assignments will be lost when the courses are deleted after the retention period.