Link to External Data Deleted

Link to External Data Deleted

I have a Zoho Spreadsheet that I need to periodically (at manual intervals) re-import data from an external source. When I create and "Run Once and Done" the link it keeps it in the link history. I can then go back under "Manage External Links" and "refresh" that link when I need to. However, I have found that what appears to be about 1 month after creating the link, it then disappears from the list of links available in "Manage External Links". I then have to hunt up the URL again and recreate the external link.

Is that automatic deletion process deliberate? What is the criteria? Is there a way to get it to stay indefinitely?

FYI, the main reason I run it manually is due to the sensitive nature of the data. I don't want to leave the source data publicly available between updates of the Zoho Spreadsheet.