One thing worth checking: the date placeholders in the upload filename and the delete-after-upload option are features of the export/graph upload job itself, not of a generic SFTP service event. The official Meteobridge wiki documents both only in the export upload section (Meteobridge NANO SD page), while plain FTP/SFTP/Proxy-SFTP service events upload a referenced file as-is. So if the upload is currently defined as a Proxy-SFTP service event watching the export folder, you would get exactly your symptoms: the file goes up with the literal name and nothing gets deleted. That is a hypothesis from the docs, not something I have tested myself - but moving the upload into the export definition's own upload settings would be my first try.
When a FTP upload is triggered by an export event the FTP upload should reference to "export:lastexport" as file. Doing so the delete option should work fine.