After updating the WordPress theme for Pro, my website’s CSS/Pro-Child folder was all screwed up. I had to restore the Pro folder in wp-content/themes. All looks good again. 
We’ll have an update on Monday at the latest. It can be worked around by using the Starter stack.
My site’s CSS was very screwed up by this update as well. Isn’t this the kind of thing you’d want to issue an immediate warning about, and/or a patch to fix this. If I’ve made changes to the css in my child theme and that is now somehow overwritten, why would restoring a pro folder help the situation?