InDesigns packaging is not bug-free for data merge documents.

You can find a good article on indesignsecrets.com https://indesignsecrets.com/traps-packaging-data-merge-files.php

If you use MyDataMerge’s packing instead, MyDataMerge will take care to include ALL images mentioned in the used datasource, it will include the datasource, the layout and so on.

Official MyDataMerge Team