SUMMARY
During a session of uploading hundreds of photos and videos, I encountered two specific files for which upload to SmugMug fails.  The two files upload fine using SmugMug's web UI, but fail from digiKam export.  Other photos in the same folder taken by the same camera upload fine.
Perhaps there is something about these files or their metadata which is causing a problem with the SmugMug API or how the API is used, but there is insufficient detail in the console logging to identify a problem.


STEPS TO REPRODUCE
1. Select one of these files.
2. Click Export -> Export to SmugMug...
3. Select Album for upload destination.
4. Click "Start Upload"

OBSERVED RESULT
Error dialog appears.
Dialog title: Uploading Failed -- digiKam
Dialog contents: 
   Failed to upload photo to SmugMug.
   Connection closed
   Do you want to continue?
      Yes      No
Logging in console after clicking "Start Upload":
unknown: slotStartTransfer invoked
unknown: d->currentAlbumID -1
Digikam::DBInfoIface::itemInfo: Database Info populated for QUrl("file://[path...]/[filename].jpg")
unknown: url to upload  "https://upload.smugmug.com/"
unknown: slotStartTransfer done
unknown: error code :  QNetworkReply::RemoteHostClosedError error text  "Connection closed"



EXPECTED RESULT
Photo uploads successfully.

SOFTWARE/OS VERSIONS
Windows: 
macOS: 
Linux/KDE Plasma: 
(available in About System)
KDE Plasma Version: 5.24.7-0ubuntu0.1
KDE Frameworks Version: 5.102.0
Qt Version: 5.15.7 (built against 5.15.7)

ADDITIONAL INFORMATION