ZynAddSubFX No Sound on MixBus 5.1 (Linux)

[acakerlund]

So my issue is, I've loaded up some MIDI files for a song on MixBus, and whenever I try using ZynAddSubFX on any of the tracks, I get no sound. The plugin is working fine, since when I open the virtual keyboard and click on the keys, it produces sound. But it is not generating sound from the MIDI track. All other synths I've tried are working fine, so I'm kinda clueless here.

I'm using Ubuntu MATE 18.04, I've tried with both JACK and ALSA, LV2 and VST plugins, exact same results in all scenarios.