I recently bought a Raspiaudio audio+ V2, and I mounted it on a Raspberry Pi 0W (first model), with a fresh RaspberryPi OS install.
I then configured the sound card with the command:
wget -O - script.raspiaudio.com | bash
Machine rebooted, tested audio and I can hear both channels on both speakers.
I tested various setups to exclude malfunctioning audio cables/speakers, but the issue seems to be confined to the RPi/sound card.
I also checked both the 3.5 mm jack and the RCA output and they both show the same issue.