Hi @nanpoulos - thanks for reaching out. This issues is connected to the issue noted here: Help! The image files aren't loading. Any idea why?.
As a suggestion, in projects, external images will appear on published sites but not in the Preview. We have noted the issue and are working on a fix so that external images appear in the Preview as you expect based on your feedback.
Similar to the other issue, I’m going to leave this feedback open so that I can reply back once we have a fix implemented.