i guess that the stream gets corked (test: pactl list sink-inputs while streaming vlc) . Mentioned at the end of this thread
Comment out load-module module-stream-restore in /etc/pulse/default.pa
And you should add "listener": { "mute_during_output": false, ...
to the listener in mycroft.conf (either sys or user, whichever carries the entry).
While this (the muting/unmuting/volume situation) is running pefectly well with “pulse_duck” : true, i would’t know if this is still the case if no ducking is active 
Though i also wouldn’t know why anyone should run Mycroft without “pulse_duck”:true (given the user pushed everything to pulse)