WordPress 4.9.5 Cornerstone 3.0.4 x 6.0.4
I developed the website as http://domainname.com and when it went live it was changed to https://www.domainname.com.
I used Better Search Replace Pro to do the rename. A page will show secure in Chrome. If you do an f12 inspect element on an image url you will see https://www.domainname.com/image name. However, if you "save in Cornerstone - even if you do not make an actual change to the page, the page is now shown as unsecure in Chrome. Then if you do an f12 inspect element on the image you will see http://domainname.com/image name. I kid you not!
This has been occurring and I thought that it was a url change missed by Better Search Replace Pro, so I ran the url change again and urls were updated and the pages all showed as secure in Chrome. So it appears that Better Search Replace Pro is changing the urls, but then when Cornerstone updates the page some how the orginal image url is saved.
I am now going into Cornerstone and removing the image that keeps changing urls and adding in a replacement image, and then saving via Cornerstone and this is correcting the issue. I hope once and for-all on this site. However, this is a serious issue.