Win11, transfers via SFTP to a Dropbox folder doesn't compute

[olaviinha]

Describe the bug
"Transfer incomplete" notification + Transfers window becomes unresponsive when downloading files to Dropbox.

To Reproduce
Steps to reproduce the behavior:

1. Open Cyberduck, latest version (updated just now), on Windows 11.
2. Connect to server via SFTP.
3. Select a number of directories in server and drag them to some directory (inside Dropbox) in Explorer to download.
4. After a short while Cyberduck sends a Windows push notification "Transfer incomplete". Later also encountered "Access denied" and "Unable to delete" errors. The last one scared me, as I wasn't trying to delete anything anywhere.
5. At this point transfers seem to continue as usual, but the Transfers window is unresponsive from here on out.
6. Trasfer freezes at "2 seconds remaining" or "3 seconds remaining" and never completes.
7. Only way out is to kill Cyberduck.
8. Observe no errors recorded about incomplete transfers in cyberduck.log

I have now tried this a kazillion times with different users, different numbers of dirs (500MB-1,2GB), possibly doing something else a little differently, but I can't figure out what goes wrong, -or- whether or not those transfers in reality are complete or not (I'm not going to go through 1,2 GB of data manually to check).

Expected behavior
A) There should be no incomplete transfers.
B) If some error really occurred in transferring some file, I should know which file(s) was incomplete.

Desktop (please complete the following information):

• OS: Windows
• Version 11 (10.0.26100 Build 26100)

Log Files
Sorry, can't. What I can tell you is that there is zero ERROR or WARN in the log, even with debug log enabled. I could not spot anything referring to any incomplete transfers.

Additional context
My first guess would be there are no incomplete transfers in reality, and this is some more interesting bug.

UPDATE: This appears to have something to do with downloading to Dropbox (updated issue accordingly). My local Dropbox is on an external HDD, but I have a whole bunch of those same external HDDs: if I download to another one, it works, so I don't think this is some "bad disk" issue. Also never encountered any such errors with other apps & Dropbox, e.g. FileZilla or when encoding large video files directly to Dropbox. Downloading to any dir in internal SSD or external HDD that is not under Dropbox, works fine, no problems what-so-ever.

[olaviinha]

Workaround was, yes you guessed it: to download to any directory that is not in Dropbox (and just move to Dropbox after that in Explorer if needed). No problems what-so-ever.

[dkocher]

I suspect the error to be related to the Segmented Downloads feature.