Bose headphones left speaker not working with iPhone

Hi there,

My Bose wireless headphones usually don’t work in the left speaker (when listening on my iPhone) they always work in the right speaker.

if I connect using Bluetooth to my tv both speakers on my headphones work fine. If I connect the headphones to my piano with a wire both speakers work fine.

They used to work ok previously, but that was sometime ago. I have tried playing from both Spotify and the iPhone Music app.

Tonight both speakers worked fine for about ten minutes but again now just back to the right one with intermittent sound from the left.

Any suggestions most welcome :)

Thanks

Mark

I have an iPhone 12 Pro latest firmware.