NUENDO 11 no OMNISPHERE vst audio output via IAC bus

Just updated from nuendo 10 to 11. Nuendo 11 disables audio output of Omnisphere 2.8.2 vst instrument (signal on Omni vst channels, no signal/sound on stereo output channel) when running my controller through an IAC bus (tuning software). Interestingly, this seems to be a new conflict with the Mac IAC driver (virtual MIDI bus) because this bug resolves with (non-virtual) MIDI connection. Has anyone found a work-around?
Mac OS Catalina