I have a playing card layout that loads all it's content using data merge. I have a spreadsheet exported from Google Sheets to CSV. The spreadsheet has about 20 fields, a few of them pull graphics. My workflow is that I create a merged document from this file where each page is on it's own page and save the file. Then I place the merged document in a "gang" layout in a separate file where I place the pages from the "merged" doc abutting one another to make a grid. Then I export the pages of this "gang" document as PNG files that I then import into software that generates cards in a vitural environment. I use this workflow on a regular basis. Sorry, that is all set up.
My problem is that with my current layout, data drops out during the step of placing the "merged" doc pages in the "gang" document. Almost all the data is there, but three fields which contain the same kind of graphic files drop out. The files that should appear are simple little 2-color symbol PNGs. They are present when I view the original "card" document, and also in the "merged" doc I generate from the card doc. But when I place the merged pages in the "gang" layout, the symbols have vanished. I assumed it was a memory issue, so restarted with just InDesign open. I then tried generating a fresh merged doc and importing it into the gang doc, but that didn't work. I ended up having to manually paste all the symbols one-by-one on 120 cards in the gang doc in order to be ready for a meeting. My computer specs seem sufficient for this, or is too much processing required of InDesign to keep track of all the pages and linked graphics. I guess the next thing I'll try is exporting the symbol files are JPEGs rather than PNG. They symbols are made in another InDesign doc and exported as individual 10 x 10 pica pages in PNG format. I do the same thing with a few other types of simple graphics. Let me know if you have any thoughts.
I am using
InDesign 15.1.2 on a Macbook Pro 15" 2.4 Ghz Intel core i9, 32 GB 2400 MHz DDR4, 10.14.6