I see still that there is mixed content error as some of the assets are loaded from the
HTTP protocol. But I am not convinced that the problem is caused by that.
Anyway, kindly use this plugin to force the SSL retrieval of the assets:
But, I also suggest that you check for possible plugin conflicts. Kindly deactivate all 3rd party plugins except Cornerstone and check the case.
Finally, I suggest that you follow the steps mentioned in this article:
I clicked on the Skeleton mode in Cornerstone:
It seems that the elements are in place and the problem is the preview:
Hope it helps.