upon bluetooth connection, it is possible that the volume sync communication between your headphones and ios device is not made. in such cases, volume up and down will work, but will not display accurately on your device.
Volume indicator out of sync between device and headphones
Applies to:
Turn the headphones off and on.
In May 2013, a software update was released to assist with this issue. Visit Bose® system update center if you need to update your headphones