In case the linked document(s) or note(s) is not contained in the backup file
The message will display if the linked document(s) or note(s) is not contained in the backup file. Please make sure that all the liked documents are selected or dismiss the message if you don't need to maintain links between documents.
In case the messages are displayed even though you select all the linked documents
The message can be popped up even though all the linked documents are selected for backup. This is a bug and links won't be missed if you select every linked document when backup.
How to backup and restore your data