It looks like you’re probably using version 2.0.3.3 (or 2.0.2.1) both of which are quite stable, but not the fasted versions around. But yes, the initial counting can take quite a while if you have lots of small files.
Of course by now I’m assuming the backup has continued on and finished, but in case you’re still curious…
There is also some “leeway” in the progress bar when it may still say “Counting” even though Duplicati has moved on to the next step of the process.
This post is a about a different progress bar message not quite showing the current actual processing, but the steps in there might help you double check if Duplicati really is still counting or has progressed beyond that and simply not updated the progress bar.