I just got a Z3 compact. I switched from a Moto X that did not have any bluetooth issues (which is still in my possession in case I can't fix this).
Anyway, when I connect to my Pioneer MVH-X560BT stereo, music will play but the audio will drop out completely every few minutes. The audio will go out for around a second. It's not lag because the song doesn't also pause when the bluetooth audio drops. After a second audio will return. I have tried many apps (Walkman, Power amp, google play, spotify, etc.) and they all produce the same occasional pause. I have used a few different phones with this stereo and have never experienced this issue.
I bought my Z3c online from someone who had unlocked the bootloader and installed a custom ROM. I found out how to install the stock Sony rom with Emma and thought that would fix my bluetooth issues. It did not. I doubt an unlocked bootloader would affect bluetooth.
