Many of the channel streams are doing with 3rd party providers who occasionally go out of service. If you were able to stream a channel and it stops then please try again in a few minutes and it may start working.
Sometimes, there may also be limited bandwidth to play a stream or it may stutter. In this scenario, you could move closer to your wifi router to see if that improves the stream quality.
A number of channels are geo-restricted and are only available in particular regions.
If you have missing audio, please check the volume or mute settings for your device.