In the new Photos.app application, the export of photographs to other services is via the OS X extensibility feature. Sharing one picture to Flickr shows the picture's filename as the title and empty description and tags even though the pictures had these three fields filled in the 'Info' window. This metadata was exported fine with iPhoto which had its own sharing mechanism so this issue is either with Photos.app or with the extensibility feature of OS X. How can I upload pictures from Photos.app to Flickr without having to retype all the metadata for each one of them?
Nearly a year later you would expect Flickr integration to have improved. As of February 2016 I have the exact same experience. To investigate further I opened this forum thread:
I contacted Apple about the inability of Photos to upload titles etc. After admitting there was a problem, the technician told me they would get back to me! No news since then.
Photos seems to be a very inferior software compared to iPhoto. I guess we will have to wait for an update with "improvements". The glitches and mistakes in the "improvement" may be even worse! Lol!
have you tried Flickr Uploadr? you can download it from here: https://www.flickr.com/tools/
I just tried... it automatize the uploading but as far I'm see did not export tags and titles.