Just tried logging into D8 core and received this. I was on home and used the sidebar login. This issue does not appear on
Twig_Error_Runtime: An exception has been thrown during the rendering of a template ("A stray drupal_render() invocation with $is_root_call = TRUE is causing bubbling of attached assets to break.") in "core/themes/bartik/templates/page.html.twig" at line 148. in Twig_Template->displayWithErrorHandling() (line 328 of core\vendor\twig\twig\lib\Twig\Template.php).
node?destination=/drupal8/node is the one I see after the submit.
The login form also has a reCAPTCHA attached - just for completeness.