They should have you do resets, check firmware and if it still fails and you can't try other soundbars, call it defective and arrange for a return to the shop to get something else.
Bob
I recently bought a Yamaha SRT-1000 sound bar to use with my Samsung UN55F7050AF Smart TV. I connected the sound bar to the digital audio out connection, and set the Samsung to external speaker. I immediately noticed that the audio was lagging significantly behind the video. This lag was consistent for broadcast TV, Netflix, and Hulu. I noticed there was an audio delay set to 30 on the TV so I set that to zero on the TV. Still had a lag. I checked the checked the audio delay on the sound bar, and set this to the lowest available setting as well, and STILL got a lag. To check and see if this was due to the TV or the sound bar, I connected the sound bar to my Sony Blue Ray player and got no lag. This leads me to believe that the issue is with the Samsung Smart TV because there is no lag with the Blue Ray player. I have seen similar threads that all point to issues with Samsung Smart TV audio lag. Some of them are call lip synch issues. If I have reduced the delay to zero, what else can I do, other than to return the TV?

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic