Answer
Export the Lobby as either Full Format XML or a ZIP archive, then manually remove the duplicated Data Source entries from that export before importing, or after importing by re-exporting, editing, and re-importing — editing the ZIP archive directly is usually the easiest approach, since duplicated Data Sources are easy to spot there by their identical file names; keep just one copy of each and remove the rest. The same cleanup can be done directly in the Full Format XML file instead, but that needs to be done carefully so the edit doesn't break the file's structural validity.