Working with a client they are having a very odd issue that I only see in their tenant.
Employee gets an email with an attachment.
Employee clicks on the attachment and choose to save to their OneDrive
Employee then from Outlook clicks on the View in OneDrive option
For this client, in their tenant, OneDrive is opening in Classic OneDrive as opposed to Modern. They are configured to run the Modern view and if they navigate to OneDrive via the Waffle, they get the modern experience.
Some other odd issues are that the favicon is different for the two views. One is showing the SPO favicon and the other is showing the OD4B favicon.