The programme mix and the way multichannel sound reaches your speakers can make dialogue harder to hear; this is different from a completely silent stream.
Why this happens
Film and television sound can contain a much wider range between quiet speech and loud effects than an ordinary news programme. A surround mix also carries information across several channels, and the result depends on how the player and audio system reproduce or combine them. If voices are disproportionately weak, compare the available stereo track or a supported stereo output before assuming the source has no dialogue. Turning the master volume up may only make the next effect louder.
Use a short scene with both speech and music so each change has the same reference. If your device provides a documented dialogue or dynamic-range setting, compare it at a normal listening level; the label and effect are platform-specific. Apple’s Reduce Loud Sounds option is one example, not a setting every IPTV player contains. Keep the audio track, output format and soundbar mode in your notes. If another soundtrack sounds normal, that difference is more useful than repeatedly changing the television’s picture or network settings.
A useful way to work through it
Compare a stereo track or output if the source and equipment offer it.
Test one documented dialogue/dynamic-range option on a familiar scene.
Record the track and output mode, especially if only one mix has weak voices.