I wanted to report a bug with the progressbar component. It seems to manifest itself when the progress bar is included in a popup dialog window, rather than in a regular tab.
The progress bar itself does not update unless you physically move the dialog box by clicking and dragging the title. This then seems to spur it on to update.
Switching the open style to tab immediately fixes the issue.
I’m afraid I won’t be able to provide a sample app to replicate the issue, but I hope it should be straightforward enough to replicate.