Sorry about the response lag. I've narrowed this down a bit more meaningfully, though I've got a lot of test cases yet to go through.
I didn't realize how narrow a niche my use case really is.
The most reliable case thusfar is:
From: Windows local machine
To: Linux remote machine, file already exists in destination.
Attempting to update the remote file reliably cause it to hang as described. I WILL get an overwrite confirmation dialog if appropriate. But "overwrite" will just close the dialog and put me back in to the individual file copy dialog.
Elapsed time will continue to update and I can hit "skip" to move past that singular file.
Windows -> Linux (remote) new file: works
Linux (remote) -> Windows new file: works
Local new/overwrite: Works.
Here's the options on a 3 file copy and the queue shot, just in case.
Weird stuff.