I've been using their Flickr Uploadr app for Windows, since the old interface. It's a lot more stable than uploading via their webpage. It uploaded my latest pics fine to this new Flickr.
To anyone having trouble uploading to Flickr, take WNG's advice and use this app. I've been using it for a couple of years. It won't bring the old Flickr back, but it is infinitely easier to upload to Flickr. Even when it was the old version, I couldn't stand the uploader their website offered. I was worried it wouldn't jive with the new Flickr, but it is the one thing that has remained the same...thankfully.
http://flickr-uploadr.en.softonic.com/download