Acquia varnish cannot cache files >10MB as per https://docs.acquia.com/acquia-cloud/performance/varnish/files/ To find for those >10MB files, search from the sites/default/files: 1find ./ -type f -size +10M -exec du -sh '{}' \; -print|grep -v ^\./| sort -n

Changing group ownership of the files in "sites/default/files". More details in https://www.drupal.org/docs/7/install/setting-up-the-files-directory