Loss of volume in one AirPod

This morning during a workout I noticed that my right-side Apple Airpod has significantly reduced volume output than the left-side Apple Airpod.

I have tried the following, with no improvement:

1. Settings > Bluetooth then Forget This Device, and then re-pairing my AirPods
2. Taking the left-side Airpod out of the case, connecting it to my iPhone, inserting in-ear then playing music. Then taking the right-side Airpod out of the case, inserting in-ear
3. Checking that the Volume Balance in Settings > Accessibility > Audio/Visual is centred
4. Following the cleaning instructions for cleaning debris in the mesh 
5. Connect my Airpods to another device (iPad) and noted that the same issue occurs
6. Connected my wife's Airpods to my iPhone and noted that hers do not have the issue

Are there other troubleshooting methods I could try? I have not had this issue occur before. I bought the AirPods in April 2019.