Are you right-clicking on an image? I've found that if you click on a different asset type (text box, or other) it offers the drop-down you see where you can segment and replace with snippet, but when you right click an image or image-box it provides different options:
The Email 1 vs. Email 2.0 might be the issue here -- I'll do some more testing, but not sure.
As for Images -- I had some issues with previews when I first used Content Ai as well. Basically the RTP server and the main Marketo server were different for me and that caused some authentication issues. Support was able to migrate them both to the same server in order to generate previews (however my issue was more on the deployment side than on the preview side, so this may not help)
As for the 'enable predictive' I wouldn't be surprised if this was tied to the image preview error you're receiving -- I'd get that fixed first and see if this resolves.