This is curious, could you please send a screenshot of the error you see when the download fails?
A weak internet connection should not negatively impact the updater, it should attempt to recover when there are hiccups in the connection.
An alternative way to get this update is to download the full installer and simply run it overtop of the current, this will effectively update the software. You can download the appropriate product here: https://www.tracker-software.com/product/downloads
As for the dual progress bars, this is commonplace among many installers, the upper bar displays overall progress of the installation, the lower, is the progress for the current portion.