Hi merula,
In an algorithm like Diatonic, the Pitch Mix parameter serves to adjust the level of each voice relative to each other. When the H9 is connected in stereo each voice gets panned to one side. For equal volume for each tap, the Pitch Mix parameter should be in the middle where it says A10+B10. If you have it fully clockwise, for example, you will only hear one voice, the B voice that is panned to the right. This could be what you are experiencing because disconnecting either output will only render the B voice if Pitch Mix is “all the way up” instead of in the middle. Can you check that setting?
