I keep running into this constantly. Express notifies me that full coverage of North America 2017.30 is available for updating on my various nuvi devices (1490, 3490, 3790), as well as the FM traffic database, but this map update has already been installed. This happens on the latest version 4.1.30.0, the Mac version, but also happened previously with older versions.
Also, it keeps wanting to install the optional updates, especially the vehicles, which I've installed numerous times and doubt that they're actually changing all the time.
Another problem is that once the updates are installed again, the bubble showing that there is a pending update on the main device list screen does not disappear.
Another problem is that after installing the updates, the option to eject the Garmin device from the device screen is greyed out, even though the Garmin is still mounted, and shows a disconnection error when I disconnect the cable.
Is anyone testing the Mac version of Garmin Express before release? The answer is no.