In case you have moved your Confluence server from one domain to another domain, previous versions of the app were able to find the locally stored scripts none the less.

For instance a script at https://old.example.com/confluence/{path.to.an.attachment}/whatever.js would be found even if the same Confluence server has the script now at https://new.example.com/confluence/{path.to.an.attachment}/whatever.js.

The reason for this is that the server simply looks if there is the attachment without checking the base URL. With this version those scripts will no longer be found.

Therefore, you need to check that all URLs pointing to an attachment do have the correct base URL. The correct base URL is the base URL of your Confluence Server.

This is a very special issue that very likely has no effect on your installation. It is highly recommended to check them! Otherwise some of your Userscripts userscripts may not work after the upgrade.!