Diagnosis
This is caused by the Auto Power Down feature. It is enabled by default. The soundbar will power off after approximately 20 minutes if it does not detect a valid audio signal above a certain threshold.
How to Fix It
Disable the Auto Power Down setting. On the soundbar remote, press and hold the 'SETTINGS' button for 3 seconds. Use the volume up/down buttons to navigate the menu on the soundbar display until 'APD' appears. Press the 'SOURCE' button to toggle the setting to 'OFF'. Press 'SETTINGS' again to exit.
If That Didn't Work
The issue may be a weak or intermittent audio signal from your source device. Check the HDMI ARC or Optical cable connection. Ensure the TV's audio output is set to PCM or Bitstream, not 'Auto'. A fluctuating signal can fail to keep the soundbar awake.
Heads Up
The 'APD' setting resets to 'ON' after a full power loss. If you unplug the soundbar, you will need to disable this feature again.