Good day! I do not know the problem as such, as I do not operate the monitor with a soundbar. However, please bear in mind that when you select audio output to the monitor, the audio data is transferred via HDMI and the sound output built into the monitor is addressed (audio out socket). Although the sound bar is connected to the monitor via USB, it cannot be addressed by the monitor because the built-in USB hub connects the devices connected via USB to the lap. Consequently, you have to switch the sound output on your MacBook to the soundbar (via the selection menu on the speaker icon at the top right), even if you have connected it to the monitor. If you don't want to do this, you have to connect the Soundbar to the monitor via audio cable. I hope this helps.