Storyboard doesn't load (keep loading) Xamarin.ios VS 2017

My storyboard file stopped showing, I tried:

1. Disconnect then reconnect to my Mac.
2. Clean and rebuild the project.
3. Restart both devices.
4. But nothing helped.

I am using VS pro 2017 - Xamarin 4.6.0.299 and Xamarin.IOS 10.12.0.20. My Xamarin and Xcode in Mac are up to date.

I am using a powerful PC so I don't think my PC performance is the problem since before the problem I needed only 10 sec to show the storyboard.