I think what is happening is that there is a problem displaying the pdf. The web client thinks there is a pdf to display - you can tell since this is the pdf viewer and not the image page viewer. You can confirm this in the details pane, under "show advanced" (if your user has rights to it). The other clue is the thick line on the left side. I think this is the loading bar for the pdf viewer. Normally is goes by too fast to notice, but yours seems to be stuck for some reason. You can get more information from the developer tools in the browser (F12), where you might see some errors or stuck requests.