Yes, but Duplicati cannot know which files are changed and which are not. It scans ahead to find the full size of files. The number reported is the size of the files it has not yet examined. Some of the remaining files may turn out to not be modified, but there is not way to guess that in advance. The stalling happens because the upload is active and too much work is in the upload queue.
I am looking into a better way to see how to communicate this.
If you choose “Log” in the menu on the right, and then choose “Live” and set the level to “Profiling” it will show the filenames. But we could also show a tooltip or similar with more information, like the name of the current file, how far in the file etc.