Some apps don't play sound
Why some apps don't play sound and others yes?
Please make sure that the mute switch (physical and software) is not enabled. Be sure to also make sure the sound is not playing through any external accessory, such as headphones or speakers. You can also check to make sure your Cast device or TV are not muted. It could also be a DRM (Digital Rights Management) Limitation imposed by the app itself. Some apps do not allow for their audio to be captured. This is done to protect the copyrights of the content that the app is displaying. This will happen with apps like Apple Music.