The version of OSMC was the latest but the version of a2dp-app-osmc was taken from git, per this post:
as you seem to be willing to tinker with this a bit, I’d recommend you get to where we were before we made changes to try and get it running out of system mode.
apt-get install git build-essential git clone https://github.com/osmc/osmc cd osmc git checkout 27a9e28b6d7224c540424445b45da87096042030 cd package/a2dp-app-osmc make
Sam was suggesting that Den4t use the previous version of a2dp-app-osmc , which contains the system instance of pulseaudio.