Fresh install of rc4 and inspect the highlighted region with Bartik as the default theme.
No output from Classy's region.html.twig
An empty region wrapper.
Classy's region.html.twig is checking for region content using twig if which will evaluate whitespace as TRUE and as the highlighted region returns whitespace even when empty an empty region wrapper is output.
Edit: removing the Status messages block from the highlighted region results results in no region wrapper being printed.