In the 7.2 update, there is now a check in place to verify if the documents linked within PTEs are valid document links, and will display the “Unknown Document” message if the IDs of the document are not able to be identified from the portal database.
The updates does not break your document links, but the update does change the display behavior for the already broken links. In a way, this is to your benefit. These links were already broken, but since no one had TRIED to open them, no one knew.
So - how did the links get broken?
Scenario 1: At some point in the past, the document was re-uploaded to the document repository with the same name as the original document (which had been linked on a PTE island) and the option of ‘Overwrite if exists’ selected. This would then create a new document ID, breaking the document link within a PTE island.
Scenario 2: At some point in the past, a document was linked on a PTE island then the document was later deleted from the document repository. Again, this would break the document link on a PTE island.
Helpful Link: Document Sanity