Thank you for reaching out to us. I'm sorry to hear you've had some trouble with the Preview mode not showing images, but perhaps I can offer some insight.
Typically these issues are caused by caching errors - especially if you're able to see the images one moment, then they're all missing the next. After consulting with my higher level technical team, and noting the fact that we could see the images in Previews and Test sends across multiple email clients and browsers, we're quite certain the issue is cache-related on your end. Here are my suggestions for getting around this.
Firstly, to determine if the error occurring is a caching issue, I'd recommend trying a different browser, if you have access to one (i.e. Internet Explorer, Safari, Chrome, Firefox, etc.). If the images appear in one of these other browsers, then it is extremely likely to be a caching issue with the original.
Secondly, if you're using a network other than your home network (i.e. work wifi), you may want to try disabling some firewalls or other security elements to see if that resolves the issue.
In the event that this is indeed a caching issue, each browser has their own way of clearing cache without clearing your history and login info.
Please let us know if clearing the cache resolves the issue, or if using a different browser ultimately works around the problem.
If you have any additional questions or concerns, feel free to reply to this thread or create a new one, and we'd be happy to assist.