Powerbeats Pro 3 - left unit volume much weaker than right unit

Although I can adjust the balance between left and right units by going to Settings>Accessibility>Audio & Visual> BALANCE, that upsets the L/R balance of the other earbuds, headphones, and speakers that I pair with my iPhone 13 Pro running IOS 18.7.1.

I tried resetting the Powerbeats Pro 3 pairing with the iPhone again, but the issue persists.

Is there a software/firmware fix, or is this a hardware problem?