Other people have reported the issue, but it’s not clear whether it’s the ST or Amazon side. For now, put the device into a new Echo group (using the Amazon app, not ST) and experiment to find a name Alexa will accept.
For me, at least, “Netflix” is not working and putting it in a group named Flix doesn’t work, but putting it in a group named “Flicks” does work. I didn’t change the activity name in harmony, just the group name in Echo.
People are posting more workarounds in the following thread: