The most recent issues appear focused on older versions of LR, especially LR 4. Given that Yahoo is now in its death spiral, it's very unlikely that Flickr or Adobe will do anything to make LR 4 compatible with Flickr again. Two options:
- Try the free trial of LR CC 2015 / LR 6 and, before making any changes to your (upgraded) catalog, test out uploading to Flickr. If it doesn't work for you, you can revert immediately to LR 4 without losing any work.
- Try this third-party Flickr plugin. The author Friedl and his plugins have an excellent reputation, and he maintains them better than Adobe maintains the built-in plugins.
Thanks for all your help, I tried the plugin and it works. I am able, once again to upload to Flickr.