There is a bug in v5.8.1 from the Mac App Store, but v5.8.2 has finally been approved, and should be available within the hour.
V5.8.2 takes me into an endless loop asking me to login into my App Store account.
Message reads "Cookie 5 was purchased using the App Store on another computer. To use "Cookie 5" on this computer, sign in using the Apple ID and password to purchase it.
What can we do to fix this?
After a restart - and another update it seems to be fixed now... Thank You!