V14 upgrade with iframe was not loading in HTTPS

After V14 upgrade CMS pages iframe was not loading over https and throws below error in browser console.

iframe request returns 302 redirect

Mixed Content: The page at ‘https://site.io/cms’ was loaded over HTTPS, but requested an insecure frame ‘http://site.io/cms/?1&iframe’. This request has been blocked; the content must be served over HTTPS.

browsers started blocking mixed content (http over https). you need to either serve all your content/resources from httpS to fix it for all users or temporary disable this error in your browser setting for individuals