If your left earbud doesn't produce sound, check following:
1. Does it say "Power on", "Power Off", "Pairing", etc?
2. Is the LED light illuminated inside of the case?
3. Is the left LED light flashing fast when you take it out of the case?
If you answered to any question "Yes" then it seems your earbuds lost pairing. Please follow instructions to reset your Air 1s.
Below you can find two reset method depending on your Air 1 model: