When having multiple attachments on an issue, you can click on them and get a preview for image/video types and navigate through the list of attachments to the left or right. In the new issue view it is only possible to navigate a few attachments to the left, and a few to the right, this happens in different combinations of attachments available to the left and right, but it is never more than 6.

The suggestion is to allow navigating through the entire attachment list, like in the old issue view.