HTTPS causing image "insert to post" to fail.

I wonder if this isn't related to the update to the domain mapping plugin? I've noticed that when I try to upload an image on this site :

I am seeing this error in the console :

Mixed Content: The page at '' was loaded over HTTPS, but requested an insecure image ''. This content should also be served over HTTPS.

Is there something I missed? I've basically just gone to the media library and added it. This was not an issue previously.

And yes support access is on.