Hey @Anonymous I just want to be extra clear about my recommendation (I'm not sure I was before):
1. Close Fusion 360
2. In your operating system disable both the WiFI and LAN connections so there is absolutely no internet connection
3. Start Fusion 360 and wait for the application to reach steady state (in my case the splash screen took awhile to get through ~10 min)
4. Select Work Offline mode
If that data panel spin issue is still occurring after enabling offline mode (you'll see a checkmark next to Work Offline when it is enabled), I have one more suggestion that may help.
You could go through your locally cached files and locate the design. I imaging the design will be stored in the upload queue.
%localappdata%\Autodesk\Autodesk Fusion 360\****\W.Login\Q (upload queue folder)
If you locate the design in this folder, you may make a copy of the design file. Next, rename it and use the File > New Design from file command to open it. I note that you can save a local archive of your Fusion Design for safe keeping as well.
I hope this helps!
Nathan Chandler
Principal Specialist