The archive "Xcode_9_beta_4.xip" is damaged and can't be expanded My other apps work great. Downloaded directly from the Apple Developer site. 

Tried to restore the 'Anywhere' permission in Security already. Restarted already. Downloaded again already. 

Any other ideas?
I just kept deleting and downloading again, and finally it worked. Not the best experience. I think it was the 4th or 5th time.