Mixed Content error

Hi,
for a few pages I get error messages (website is running with https)

Mixed Content: The page at ‘https://www.navigation-professionell.de/gps-sportuhren/’ was loaded over HTTPS, but requested an insecure script ‘http://www.navigation-professionell.de/wp-content/themes/Divi/includes/builder/scripts/frontend-builder-scripts.js’. This request has been blocked; the content must be served over HTTPS.

Disappears after purging the cache, but the error appears again after some hours.