Share to Flickr stuck "Publishing - About 5 seconds"

I can't upload (share) photos from the Mac OS Photos app to Flickr. I set up my Flickr account in System Preferences/Internet Accounts, the Share Menu is checked there, so is Enable this account. After selecting about 20 photos and clicking on the Flickr option under the share button I get the "Exporting X of Y photos for sharing" dialog and then the Flickr settings popup appears. So far it works as expected, but after filling the popup information (I tried all combinations - set the Title only, fill all fields, selecting different Photo sets, leaving it empty) next popup with a progress bar says "Publishing - About 5 seconds" and nothing happens after that, just keeps hanging there, nothing gets uploaded to Flickr...

Any ideas why it doesn't work?

BTW, does the Photos app get rid of the "Exported for sharing" versions or are they piling up somewhere in the Photos Library?

Thanks,

David

OS X 10.11.5, Photos 1.5