MS 3.2.3 Loopback doesn't overdub after first pass

Has anyone else found that Loopback doesn't overdub after playing the first pass and hitting record to set the loop length? Occasionally, if i stop and restart playback the last dub will appear, but then i hear that next dub cut off at the loop start marker, like it quit recording when it comes around again.

I have the Loopback instances set on concert level Aux channels fed by a few instrument channels, not on the instrument channels themselves. But that shouldn't be a problem, right? Also, monitor is set to on, clock start set to clear loop, select set/patch set to do nothing, sync on and start at loop beginning on. And I start without a set loop length.

Mainstage 3.2.3

OX 10.11.3