OneDrive files disappearing

I have some users that work from home on company provided desktops. They also have office PC's. We use OneDrive for Business (part of our O365 Business Premium sub) to synchronize user data between their PC's so they can sit down at either location and have access to the same folders and files. This has worked well until now. No changes have been made to sync settings.

This morning, $user contacted me to say her files were disappearing. Her MFC is set to scan to a OneDrive folder, and Microsoft Print to PDF is also set to target these OneDrive folders. She told me the files were disappearing, and I naturally assumed she was just looking in the wrong place or had somehow changed the target folder. So I set about recreating the problem. Print a web page to PDF and scan a...