Finally bit the bullet and unlinked, to begin the process anew.
ACK! the first time through, the link failed at "downloading data."
Rebooted, then tried again, making sure to clear the "download citation media" box, and the link completed successfully. My own media is still processing.
Once that process completes (likely tomorrow), I will then try to include the citation media.
Of course, my categorization is gone, but that's minor compared to being unable to sync at all.
No news, of course, from Tech Support.