Yes the MS disappears regularly, reappears when I get into the attenuation area. Default Sound concurrency = None. And in the tests there are only 5 sounds playing
The problem appears to be the combination of Quartz+play quantized+MS as player+attenuation . I need the MS to be in sync with a master clock, this is why I am using the quartz system. If instead I use directly the asset sound file with play quantized everything is smooth and super tight in timing. If I do not use spatialization/attenuation even with play quantized + MS everything is fine. Triggering an MS without play quantized, even if I trigger via subscribed events, the MS is slightly off (I work too much with audio to not realize it 
) but file is changed.