Ardour seems to recognize my plugins, but won't play them back

I have a very oddly specific problem that I can’t seem to find an answer for on Google. I have one track, my drum set, which allows me to play into it and plays back the same LV2 plugin. This one has an option on its instrument dropdown for “Plugin Provided” (see below).

My other track is supposed to go through Helm (a virtual synth) and plays back sound from Helm when I play into it. However, when I play back the “recording” none of the notes come through. It has two dropdowns: one that lets me choose from built-in synths, and the other that switches between “General MIDI” and “MIDI”. I have the mixers configured in the exact same way, just with different instrument plugins.

Am I going insane?

Would need to see your mixer, but my first thought is to check your track monitoring options as the Helm track in that example is still set to record, whereas your other track is not. This means your helm track is probably monitoring the input to the track and not the input from disk, at least in many setups (This can be changed). Try taking your track out of REC-ARM and see if that changes anything, and if not make sure it is set to monitor the DISK not IN to playback already recorded material.