text: I have a doc, let’s call it doc2. it has a cross-doc table from another doc - doc1.
  There is an images column.
  Back in source doc (doc1), lives the table with the images column, and its formula: Concatenate(thisRow.[Photos Names].[Full Image]).
  “Photos Names” is a select-list relational column where I choose images from another table on doc1, the “Files” table. That table has each file on a row. The “Full Image” column on that table is an image which resides in the doc itself (uploaded to the field).
  The table would get the images from the relevant rows and show them, and it would also show them on doc2, the target (not source) cross-doc.
  This used to work fine, until a couple of days ago, when it stopped showing the images in doc2, and now it shows "Invalid attachment value)
  It’s the same whether there is one image there or more, and, as mentioned, it worked fine.
  I think it started after the recent Coda announcements on new features regarding syncing pages and permissions changes (which I don’t use here, but the timing may be relevant)