iCloud Sync of 90,000+ photos and video stuck for days

Hi there,

[This is a cross-post from the Photos forum, as the problem may have more to do with iCloud than the Photos app.]

I'm in the process of syncing all my photos/videos to iCloud. My Photos library is situated on an external SSD drive attached directly to my Mac Mini (ie not via a hub).

The blue bar has not moved for three days. Internet is fast and functional. Any suggestions as to how I can de-constipate things? What hasn't helped: restarting the mac, "pausing" the sync.