Issues with INDD linked files failing to export to PRINT

Since latest update 18.2 I've noticed that INDD files that contain INDD linked files now fail to export to PRINT PDF. Export to Interactive PDF works.
This file is not a book file but a packaging file so I use a linked INDD file for shared nutritional panel data (for cans, cartons & client presentations) and I've been doing this sucessfully for years.
This isn't a broken link, corrupt font or colour issue. After eliminating every element in the packaging file I worked out that it is the linked indesign file that is the problem AND If I open the linked file and export a PDF it works just fine! This leads me to believe that there is nothing wrong with my files but something has gone awry with linking indesign files within indesign files and the export to print pdf function during the lastest update.
When I try and output to print the error message is very vague.
It just says:
Background Task Alert
1 problems was found with a background task:
> Export: "my file name appears here" (1)

With regular tight deadlines I am really in a crunch with this one.