I also read somewhere that if you don't use Google Home to turn the TV
on, then you have to tell Google to "tell harmony to" for any command to
work.. I have not actually tried this as I always use Google Home to
turn my TV on..
I was having the same issue but found that Google changed the command to
"increase the tv volume" or "decrease the tv volume" and you can specify
a value to move the increase or decrease by.. Previously, I would just
say "increase the tv volume by 5"...