Let’s be clear here, I’m not sending notes from two sources to the same voice on the same channel. Hermod is. If Hermod called the output “midi thru” I’d be 100% with you, but it’s not. It’s a “midi out” and as such, Hermod should be responsible for the notes coming out of it.
Also, I tested it with different channels. If I set Track 1 to output MIDI channel 2 and set my synth to listen to channel 2, I still have the same problem. Hermod isn’t passing the channel 1 (keyboard) and channel 2 (loop) to the synth separately, it’s combining both the input and the loop into a single channel 2 stream and passing that into the synth.
If Hermod is going to combine multiple things into one stream of notes, it needs to be smarter about how it does it.