Hi there. I'm having a similar issue. I upload the image in the Design Studio. It works totally fine.
But when I'm editing an email the image is not listed as a choice when I click the radio button to insert it from the Design Studio. It just isn't there. I've checked all of the folders and I can't find it.
So I have had to go back to design studio, copy the URL of the image and then put that in the email editor. Any ideas?
The thread you're replying to is about two years old, you might have better luck getting responses from the community if you open a new question