Stuck "importing photos..."

After trying many different possible solutions unsuccessfully (restarts, unlink and relink, complete reinstall, etc.) my problem (and solution) turned out to be similar to Paul P.'s, above.

When I looked at my list of files in the Camera Uploads folder, I realized that a chunk of three days of photos were missing. Everything up to that day was fine, and several days after that were okay before importing halted and began to hang a few days ago.

Unlike Paul, all of my photos had imported into the OS X Photos app, even though they didn't upload to Camera Uploads — so I knew I had a backup, but I couldn't easily identify which one might be corrupt.

What I did was select and delete on my iPhone all the photos that had not loaded to Camera Uploads. There were 68 in all, including a 22 photo accidental "burst" photo. I then went into Trash on my iPhone and restored 4 of them, unplugged my iPhone and plugged it back in, and ... the progress bar on "Importing photos" did advance, and the 4 photos uploaded to Dropbox! (It took more than a minute.)  repeated this, gradually increasing the number to 8 and then 12, unplugging the iPhone and replugging it in each time, and each time they uploaded, quicker than the first time. I did the "burst" last, and it too uploaded. Things seem fine now.

I hope others with this problem find this useful as well. (And Dropbox, in trying to come up with a way to prevent this from happening.)