So, after a couple of additional unsuccessful attempts to update to 8.2.4, I decided to uninstall X1---despite the X1 updater's advice to the contrary---and after doing that, I again launched the installer. It completed successfully on the first go. Don't know why X1 advises against an uninstall prior to updating, but in my case uninstalling allowed the X1 installer to successfully complete.
:Win 7, 64-bit
:Win 7, 64-bit