Hi @jorf
Welcome to the Sonos Community!
I tried to setup an announcement as part of an Alexa routine on my own Sonos system, and nothing happened. A manual announcement from the Alexa app did work, as will voice announcements.
My colleague was able to get an announcement from a routine working, but only if he included an action (like turn on a light) or a second announcement in the same routine. I was unable to reproduce this.
Clearly, something unusual is going on which we will investigate. Thanks for letting us know.
I use the announcements in many of my Alexa routines, so I appreciate it that you are looking into this problem.