Sorry you had such a painful time updating! Since the update through the app is failing, I'd suggest quitting XD, uninstalling via the Creative Cloud desktop application, and then reinstalling. If you still have problems, you might want to try uninstalling XD using the Creative Cloud Cleaner Tool, then installing via the Creative Cloud desktop application.
Hope that helps! Let us know how it goes.
Uninstalled, reinstalled. And now old files open too. Very happy now.
PS. I like XD very much, it's superfast wireframe tool. Especially now when there's export to PDF.
Awesome! Thanks for letting us know you were successful. I'll pass along the kudos to the team.