OK Looks like this could be due to me running the config tool on macOS 10.12. When you launch the tool is does mention that it is compatible only up to macOS 10.11, but allows you to carry on anyway.
It seems that the image may have gotten corrupted during flashing, although it reported that it had been successfully updated.
Anyway, I re-ran the firmware image update on Windows 10 using the Win64 version of the update tool and the Edison is behaving properly now.
Hopefully there will be a compatible version of the tool for macOS 10.12 soon.