Our S 100D completed production in mid-February (with the 17.7.2 release installed) and spent a month in transport and waiting for the EPA hold before delivery. During that time, the 17.9.3 release was distributed, but was not installed in the car while Tesla had it at the Service Center.
After delivery, I took the car back to the Service Center and after several hours, they were unable to get 17.9.3 to install and ordered a new processor module. When I got home, I did a "Power Off" and rebooted both the dashboard and console processors - and within an hour, my smartphone showed our S 100D had a new update available - and 17.9.3 installed successfully on the first try at home.
It's not clear why 17.9.3 installed in our garage after Tesla was unable to get it to install at the Service Center. Getting it to install may have been due to the Power Off/reboot sequence I did at home or might have needed something Tesla did at the Service Center while trying to get it to install there.
Yesterday afternoon, after returning home, I received a "software update available" message on my smartphone - and was able to install the 8.1 release on the first try. So whatever was preventing 17.9.3 from being installed appears to be cleared up now.
If you have a new S/X and still running 17.7.2 or 17.9.3 and don't receive 8.1 in the next few days, I recommend trying the Power off/reboot sequence and if that doesn't work overnight, then contact Tesla's phone support for assistance.