Comment 5 for bug 1438510

I had the same problem and for several months I have tried all possible solutions I could find to no avail,... until today!

I found the solution in post #17 in the following https://bbs.archlinux.org/viewtopic.php?pid=1526534#p1526534 (tnx SimFox3)

What I did:

# First copy the files I edited

    sudo cp /etc/bluetooth/audio.conf /etc/bluetooth/audio.conf_tmp
    sudo cp /etc/pulse/default.pa /etc/pulse/default.pa_tmp
    sudo cp /usr/bin/start-pulseaudio-x11 /usr/bin/start-pulseaudio-x11_tmp

#Edit /etc/bluetooth/audio.conf

    sudo nano /etc/bluetooth/audio.conf

This is in my audio.conf

    # Configuration file for the audio service
    # This section contains options which are not specific to any
    # particular interface
    [General]
    Enable=Gateway,Source

    # Switch to master role for incoming connections (defaults to true)
    Master=true

    # If we want to disable support for specific services
    # Defaults to supporting all implemented services
    #Disable=Gateway,Source,Socket
    Disable=Socket

    # SCO routing. Either PCM or HCI (in which case audio is routed to/from ALSA)
    # Defaults to HCI
    #SCORouting=HCI

    # Automatically connect both A2DP and HFP/HSP profiles for incoming
    # connections. Some headsets that support both profiles will only connect the
    # other one automatically so the default setting of true is usually a good
    # idea.
    AutoConnect=true

    # Headset interface specific options (i.e. options which affect how the audio
    # service interacts with remote headset devices)
    [Headset]

    # Set to true to support HFP, false means only HSP is supported
    # Defaults to true
    HFP=true

    # Maximum number of connected HSP/HFP devices per adapter. Defaults to 1
    MaxConnected=2

    # Set to true to enable use of fast connectable mode (faster page scanning)
    # for HFP when incoming call starts. Default settings are restored after
    # call is answered or rejected. Page scan interval is much shorter and page
    # scan type changed to interlaced. Such allows faster connection initiated
    # by a headset.
    FastConnectable=true

    # Just an example of potential config options for the other interfaces
    #[A2DP]
    #SBCSources=1
    #MPEG12Sources=0

#Edit /etc/pulse/default.pa

    sudo nano /etc/pulse/default.pa

comment out (with an # at the beginning of the line) the following line

    #load-module module-bluetooth-discover

#now edit /usr/bin/start-pulseaudio-x11

    sudo nano /usr/bin/start-pulseaudio-x11

and after the lines

    if [ x”$SESSION_MANAGER” != x ] ; then
            /usr/bin/pactl load-module module-x11-xsmp “display=$DISPLAY session_manager=$SESSION_MANAGER” > /dev/null
    fi

add the following

    /usr/bin/pactl load-module module-bluetooth-discover

#Restarted and I was finally able tot switch to A2DP

Hope it works for you too.