@Anonymous User
I don't own a Samsung TV, but i had a similar problem with the Amazon Prime Video inbuilt App on my Panasonic smart TV.
On my setup, the way i managed to get sound out of my Sound Base from the TV App was to change the optical out / spidif settings from Auto to PCM in my TV sound settings.
All my inbuilt Apps on my TV play sound perfectly fine now apart from the Netflix App on the TV where for some unknown reason i can't get sound to my Sound Base either using the HDMI ARC feature connected to the correct HDMI ARC port on my TV or using the optical out.
The only way i can get sound from the Netflix App inbuilt to my TV was either use the TV on board speakers or utlize the RCA audio out or headphones out from my TV to my Sound Base 
Hopefully your fix is just a matter of having a play around with your sound settings in both your TV / Soundbar or maybe a forum member who has encountered this sound issue with the Samsung smart TV inbuilt NowTV App knows the cause and more importantly the solution how to resolve it.
Good luck.
