All attachments that are copied or moved from Jira to Confluence remain in the
<confluence_install>/temp directory (in addition to the correct attachments folder).
This happens due to a known problem in the Confluence REST API. Feel free to vote for/watch the corresponding issue CONFSERVER-41622 from Atlassian.
As a workaround you can manually or automatically delete all
attachment-*.tmp files that are older than a couple of days in the