Are you using the Alexa Virtual Switch that is a combo switch/sensor? If so, most people having been reporting that the state of the Virtual switch/sensor tracks in both ST and Alexa. However, many people have reported that the change in state on the Alexa side fails to trigger routines.
I have three virtual presence switch/sensors, one for each person in the house and one for the location mode. My ST automation changes the location mode to away when both Life360 presence sensors are not present. It also changes the virtual sensor for the location to away as well. That in turn triggers Alexa to set Guard on. Since earlier this week, it has been working successfully.