I've owned the QN90B for roughly 2 months now. 2 weeks ago I purchased the Q800C sound bar for enhanced audio.
Up until 2 days ago, the TV remote would control all audio perfectly fine meaning I didn't require the sound bar remote.
Suddenly, the TV remote volume control buttons don't control any audio output setting when the sound bar is attached to it. I.e. it only works on the tv. If output is set to Qsymphony (both tv and soundbar) or just soundbar, it doesn't work and I then need to use the soundbar remote.
weird.. never hear or seen this before. not sure if any of these helps see if they help you. first I would suggest power cycle both device. plug power of your tv and soundbar. then hold their power button on the device not remote for about 15secs. then plug back their power and power them back on again to see if they start working.
if not try to check and make sure that anynet+ HDMI CEC is turn on in the TV? lastly this is likely not relevant but if nothing helps try turn off your soundbar, then press and hold the woofer up volume button of your soundbar remote and pay attention to the soundbar indicator. see if it is set to Samsung Remote. if not just repeat the steps each time the indicator goes off until you see it says Samsung Remote then power back on your soundbar again to see how it goes. if nothing works then probably you want to reach out to Samsung for further support.