Lightroom Classic Publish Services fails to publish to Flickr; Flickr API returns error message

Two weeks ago I was using the Publish Services in Lightroom Classic 11.5 with no problem. Now I have 5 new photos to add and I keep getting an error saying "Flickr API returned an error message (function upload, message nil)" or "An error was encountered while trying to access Flickr server."

I tried removing the Authorization in Lightroom Publish, and then putting it back. 

Basic steps:

Add photos from Collection to Publish Services: Flickr: Photostream.

5 photos are in New Photos to Publish.

Click "Publish."

Wait a long time while the progress bar says it's uploading, and then the bar turns red and returns an error message.

It is also acting wonky in saying there are 3 Published Photos and then it said there were 507 "Modified Photos to Re-Publish" and then the next time I attempted it said there were 759  of those — when I have not modified any of them recently. And both the Published and Unpublished have "!" on them, and say the previous location is an external hard drive I only use for traveling, which makes no sense at all. I'm tempted to delete them all from the "Modified Photos to Re-Publish" in case that's what's causing the error, except I'm concerned that will also delete them all from Flickr, which I do not want. But if that won't take them off Flickr, let me know.

I am on Mac OS 12.4 Monterey.