html.html.twig template causes code change message to appear

After copying the system module's html.html.twig template into my theme's template folder to make some changes to the template, I received the following message when visiting any page my theme is used:
If you have just changed code (for example deployed a new module or moved an existing one) read http://drupal.org/documentation/rebuild

After following all the suggestions on the rebuild documentation page, the message still shows. Once I removed the template file from my theme directory everything worked fine. Checking the log messages, there are two listed after reloading the page:
Twig_Error_Syntax: The filter "clean_class" does not exist in "themes/custom/twigal/templates/html.html.twig" at line 35 in Twig_ExpressionParser->getFilterNodeClass() (line 573 of /var/www/drupal-8/core/vendor/twig/twig/lib/Twig/ExpressionParser.php).

Line 35 in the system module's html.html.twig template is:
not root_path ? 'path-frontpage' : 'path-' ~ root_path|clean_class,

Line 36 also contains clean_class