USB-C Multiport Adapter update not installing

I thought I had the answer to this but ...

I installed the USB-C software update soon after it was released. It reported "Installation successful" but every time I booted the rMB there was a notification to install the update. A check of the version ( About the USB-C Multiport Adapter Update 1.0 - Apple Support ) revealed it had not updated.

I finally read the instructions ⚠ on the splash screen during installation and realised that the adapter needed to be plugged in and connected to a power supply. I did this and tried installation again but still got the splash screen. I tried the installation a second time and it has finally worked.