I want to add to this that this also happened to me on two computers that I was testing the upgrade on where it immediately performed a scan after the upgrade was completed and promptly shut down the computers. The event log confirmed it was an ESET-initiated shutdown after a scan completion. This is the same as the others have reported, but not a scheduled task, and not on demand, but immediately after the upgrade. Being located 1700 miles away from the office, and during a pandemic where no one else is in the office on a regular basis, it took a full week to get someone in there to turn these computers on. Fortunately, they were computers that were not in use by anyone, so were perfect candidates for this upgrade. Of course, I can't risk updating any other computers to 7.3 until this is confirmed as resolved.
JoeC received kudos from cmit in upgrade to 7.3.2032 - computer gets shut down after scheduled scan