The issue is that it’s unclear what the “to go” number really is - which is the number of files (and size of those files) left for Duplicati to look at to see whether or not they have changed. At present the GUI doesn’t show anywhere the number of files actually changed or being uploaded.
It shouldn’t be re-uploading the same stuff. Duplicati can tell whether or not a file has changed and, if so, what parts (at least down to a 100k chunk, with default settings). It will only upload as many 100k chunks as needed to make sure all CHANGES are backed up.
This is a known shortcoming in the interface and some updates have been proposed (though not yet implemented) including my favorite mentioned here: