Why will the file attachments not open or download in my upgrade or test site without error?
File attachments in Upgrade or Test sites
File attachments are not copied to the upgrade/test sites due to disk space involved in creating copies. There is a dummy list of links to attachments that appear in the database, but the links can not be followed. As a result, you cannot open attachments that are associated with a record.
For upgrade sites, after cutover, the file attachments are available and can be opened or viewed as expected.
For more information on update changes, refer to Changes carried forward at update cutover.