Symptoms
Attachments are stored on filesystem but there isn't any attachment in the attachments folder.
Diagnosis
You can determine the missing attachments by using the Missing Attachments Report.
Cause
The attachment naming scheme is numerical so as to avoid encoding problems with operating systems.
Resolution
You can look for the attachment detail (e.g file type, attachment name) from ATTACHMENTS table.
Select * from ATTACHMENTS where pageID='<PageID>'
As attachment is stored as this structure:
Confluence 2.x:
<attachments>/pageID/attachment/attachmentVersion, you may want to run the following query to retrieve attachments of a page:
Confluence 3.x:
See Hierarchical File System Attachment Storage.