Does the TV have its' own speakers.
Use those speakers for awhile. See if they work or do not work in the same pattern.
[Side bar: We have Xfinity and have noted that there are some Xfinity commercials that go "silent". Just no sound at all while the images seem normal. Sort of believe it is some gimmick to get attention. TBD...]
Anyway, to help you, take a close look at the sound bar's connection to the TV: is the connection fully in place and solid? Have you been able to try another known working connection cable between TV and sound bar?