There are two very popular virtual devices used with Alexa, both created by @bjpierron . One is a combo switch/contact sensor. The other, called a button, is a combo switch/contact sensor/momentary button.
The dual device seems to work fine with the new V3 app.
However, the triple device, the one with momentary capability, does not work and the switch and the sensor get out of sync. Here you can see the switch is off but the contact sensor is open. 
The dual device stays in synch.
.
The out of sync issue only happens in the new app, not classic.
It might help if those who are having problems triggering Alexa could specify which DTH their virtual device is using if they know.
The following author thread has the code for both of these devices: