Sharepoint Designer Workflow Error "Stage title is empty"

I've been developing a SharePoint Workflow for a Project Server site for almost a month, everything worked fine until yesterday.

Now when I try to edit the workflow through Sharepoint designer I get an error for each Stage in the workflow that says something like: "Title cannot be empty" (I've got it in Spanish but that would be the translation).

When I accept those messages I finally reach the workflow but the stages have no name.

I've checked the stages in the Project Server and everything seems to be fine. I've also been googling it and found not this error but similar ones that point out to permission issues but the user I am using to access the WF is an administrator level user.

And apparently no permission changes have been made. Any idea? Thank you.