Add another layer of info to your command... or add YONOMI to your arsenal...
If you were today "Alexa, Tell Harmony to change to CNN" see if that works more consistently. Not just for a day, but give it a week... if you watch CNN that much...
If that does it, then YONOMI can change the command to the original one, except instead of "Turn" to CNN, use the command "CHANGE" to CNN... this helped me get through a bunch of issues with mine and My Aunt's systems.
It's not *what* you ask Alexa to do, It's *how* you ask... Just like any other woman <ducking>...