Hi
Have you tried plugging them in and holding the reset/noise cancelling button?
I found that sometimes they do this when they can’t find the device they are paired to so I would try a full reset while on charge
Here’s a link for the instructions for the reset
[link|https://support.apple.com/en-us/HT201118|https://support.apple.com/en-us/HT201118|new_window=true]
Another thing to try would be disconnecting the battery then reseating it
Here’s a guide for that
[link|https://m.youtube.com/watch?v=SBeHaqnw45w|https://m.youtube.com/watch?v=SBeHaqnw45w|new_window=true]
In your case you just need to reseat the connector:-)
After that it could be a issue with firmware or the headphones logicboard ;-{
Hopefully this helps
Any questions please ask
Thanks:-)