The problem is on google's side; had the problem for couple of days;
fixed itself and since yesterday it is back ... I don't think we can do
much.I installed a smart Wi-Fi remote control as a backup for my father
in law so he can use that when google...
I did sent feedback from within the google home app on my cellphone.
Click the letter of your name in the top right and select feedback.
Didn't get any reaction yet ...
Same problem here. Was able to change channel for multiple months and
since last friday it just doesn't work anymore. Getting exactly the same
reply from my mini as you. The Samsung Smartthings app works like
before. I suppose google changed somethin...