Adobe Captivate Could not open *.cptx ensure that the file isn't open or damaged

Dear

One of our users told us he suddenly cannot open a bunch of projects anymore.

These projects where made by a different person that left the company and the pc used to make these projects is gone. (So Dcache doesn't seem an option)

I've tried to restore the oldest backup available on the fileserver but unfortunately no succes.
Is there a way we can still restore these projects ?

As it seems we're losing days if not weeks of work to this problem and the projects seems unchanged.

So I have no idea what could've corrupted these files.

I've tried multiple pc's, captivate version is : 9.0.2.1