No sounds from any MIDI instruments
After creating a MIDI track and adding an instrument (I've tried Calf Monosynth, a-Reasonable Synth, a-Fluid Synth with a soundfont loaded), clicking on the piano roll keys does not produce any sound or meter activity. Drawing MIDI notes in the track, then pressing play doesn't either. Something is wrong with the internal MIDI routing, and I cannot figure it out.
Everything else is fine in my setup; I can record and playback audio in Ardour, and I can load Calf Monosynth in the Carla host, connect my MIDI keyboard, and make some noise just fine. Somehow I have screwed up something in the MIDI or track configuration in Ardour.
I've tried Ardour 5.8-10 on CentOS 7.