all right...seems the feature is unreliable. If i can't trust it to work i won't tell anybody to send me such messages. I'll check again in a year or so, maybe it works after a couple of firmware updates.
I received a message from Garmin today that they have released a fix via the Connect app (version 4.68) and that they can’t reproduce the issue anymore. I’m going to give it a shot during my next ride but please do report back if you do!