I've on day 4 of my first Gen 4 sensor. After the first day it's been very reliable. Yesterday I had an hour of the "Wait" hourglass followed by ???. After that the sensor kicked back in and seemed to work great. Mid-morning today I got a sensor failure alert.
Although I had some 7+ sensors replaced when they weren't working well, I think I only had 1 sensor failure in 1-1/2 years. So it's a bummer to start my Gen4 career this way. But I've got a new sensor inserted and will hope that the first one was a fluke.