CKEditor writes bad urls when Drupal core is installed in a subdirectory

For my site, Drupal is installed in a subfolder at https://www.my-site/support. In the settings.php file:
$base_url = 'https://www.my-site.com/support';

When you inspect the console on page load where CKEditor is loaded, a number of errors are thrown indicating that some resources that are called by JS cannot be found. Looking at the urls (see attached) you will note that the subfolder is being wrongly printed twice in the url, i.e:
https://www.my-site.com/support/support/sites/all/modules/ckeditor/css/c...

Does anyone have a solution? Thanks.