I have a user that has an Excel file saved in a 2013 SharePoint on premises document library (versioning is not turned on). It is a .xls and he's been using it for some time and it's password protected. All of the sudden when he opens it (in Excel not the browser), then types in the password, he's getting "SharePoint file error: data may have been lost" message and he claims now he's missing a bunch of data previously added over a period of time.
The document is quite old, created in 2010 and the user says he's opened and saved it in the past with both Excel 2013 as well as 2016 and different computers.
When I open it, I do get the same error. And when I try to do a save as, Excel crashes and doesn't save it. I was able to download it to my computer using file explorer and open it, I still get the error but I can open it.
I can go into so much more detail but before I do I want to determine if this is a SharePoint issue or an Excel / user error? I'm leaning towards the latter!