This link from Apple Support also at the top of your post. If you can't control your TV or receiver with your Apple TV Remote - Apple Support
You are up to date on TVOS?
These are the speakers in the TV and you are using HDMI CEC to control volume?
—Try a different HDMI port on your TV (not every HDMI port may be the same).
—Check HDMI settings in the TV, specifically CEC (may be called something else).
—Try a different HDMI cable
—Make sure your TV’s OS is up to date
is this happening on a certain app only? Try multiple scenarios with other apps. If it’s a particular app, this may need to be an app maker fix.