Overdrive app doesn't download

My Public Library uses Overdrive for downloading books. When I press download in this app, having selected a book in "my bookshelf" after about a second the app reverts to its front page and no download has taken place. I have tried this many times always with the same non-result. I have tried deleting and reloading the app but that makes no difference. Can anyone familiar with Overdrive help me? The Overdrive help function simply suggests check the Internet connection but I have of course done this.