OneFiercePuppy: Sure. First, go to
gog.com/account and make sure you're logged in (you should be, since you're posting). You should see your games there. If you have a lot of them, either use the arrows at the bottom of the page, or in the search bar right below the purple bar advertising GOG Galaxy type Witcher.
Once you've gotten the Witcher icon on your screen, click on it and it should expand and show you a whole bunch of files. Download whichever ones you want; at the very least, make sure you're running the 1.21 patch and download the three files for the new expansion (one very small executable, one large data file, and one smaller data file). Then you can run the executable once you have all three files downloaded, and it should find your installation of Witcher 3 and get everything working.
EDIT: I see you've edited your post while I was answering :P I have two more ideas for you, then. First, try closing your browser, then opening a new window and completely clearing the cache. If you know that's going to be a hassle, try that second, and first try to refresh your account by going to
gog.com/user/refresh Simply nothing is working. Thanks for the replies though.
I've had a quick look in the program data and theres a file called ownership.dll. I restored previous versions of it and surprisingly the option to download Blood and Wine appeared in my application.... but ofcourse "Installation failed - server problem". I'm assuming it must think I don't own blood and wine and thus won't let me download. This is completely ridicolous. If ownership details are kept on the PC and not server side I'm going to be furious. Worst security ever.