no sound with xfinity stream CBS shows

I record CBS shows like NCIS LA, NCIS NO, Magnum PI, FBI.  I record other shows from other networks but NEVER have this problem:

The sound works upon playback from the DVR like I pay for.  However, when I download onto my iphone 10s, the sound will work for awhile then cut off.  The video works.  The subtitles can be set off and on.  But the sound never comes back.  I can watch it at home, but I pay for being able to download.  Of course, I've checked the volume.  Turned the phone off and on.  Tried with and without bluetooth.  Other shows and movies that I download from xfinity work all the time, never a problem with sound.  But if it's from CBS, it's a problem.

And I've checked other download sources when this occurs in addition to the other xfinity downloads, like Netflix, Disney+, etc. and everything I've downloaded works with sound throughout the program.  What's the fix???