Volume drop after 5 seconds of audio playback

I am using a Pi4, Digi 2 Pro, DSP add-on, running HifiberryOS, to play bluetooth audio through my antiquated home stereo.  I am connecting via optical cable.  I can make the bluetooth connection via my phone and laptop.  However, after about 5 seconds of audio playback, the volume drops.  I am not running volume limiter in the HifiberryOS, but can not figure out why the volume drop is occuring.