NOTE - This issue has been resolved by a new version/update of Universal Type Client v6.1.7:
When opening a file in InDesign, users are prompted with a message that links have been modified or modified outside of the application.
"This document contains links to sources that have been modified. You can update the links now, or update them later using the links panel."
This will happen on both macOS and Windows OS machines running InDesign 2018 and Universal Type Client 6.1.6
This can be resolved by uninstalling version 6.1.6 of Universal Type Client and rolling back to the prior version of Universal Type Client version 6.1.5.
For instructions on how to uninstall the Universal Type Client please use the following link: