Ciao,
per chi ha problemi di audio, consiglio di disattivare il rilevamento di "Ok google" da ogni schermo.
A me ha funzionato
Grazie a MechaBouncer dal forum xda-developers com /galaxy-s4-active/help/att-galaxy-s4-active-bluetooth-device-t2851852
"After spending some more time testing it, I can verify that it IS in fact the “OK Google” hotword scanning from Google Search 3.6.14.1337016.arm. When it is set to detect “From any screen” and well as “From lock screen”, the audio will die after the first call over Bluetooth. Once I turned off “From any screen”, the Bluetooth works normally."