Just an update. The Preview now does not work on PCs either. One additional error I see is:
iframe.html:16
Uncaught Error: Unexpected message received by the iframe: [object MessageEvent].
Expected setup_port
at Object.initialisationMessageHandler (iframe.html:16)
at iframe.html:16
Ok, yes, I see the problem there. Thanks.
Also, the preview toolbar is not showing up on a Mac in Safari. Chrome is working now. I tried this in the incognito mode of Safari.
If your previews are working everywhere, but not in Safari, then the issue is an easy fix. Safari released an update that blocks cross-site cookies. Our preview system uses these cross site cookies to build the previews on top of your web app, so you will need access your Safari preferences > navigate to the privacy tab > deselect 'Prevent cross-site tracking'.