I cleaned up the project. There is only the routing which maps my controller (akai midimix), so I could see the lights.
I tested this with midi only and with running audio -- no difference.
After cleanup, the rate at which dropouts occur, dropped, but it still happens at constant rate while running midi out. See printout.
noteout _ port: 0, channel: 0, pitch: 18, velocity 127
noteout _ port: 0, channel: 0, pitch: 14, velocity 0
noteout _ port: 0, channel: 0, pitch: 17, velocity 127
noteout _ port: 0, channel: 0, pitch: 13, velocity 0
noteout _ port: 0, channel: 0, pitch: 16, velocity 127
noteout _ port: 0, channel: 0, pitch: 18, velocity 0
noteout _ port: 0, channel: 0, pitch: 21, velocity 127
noteout _ port: 0, channel: 0, pitch: 17, velocity 0
noteout _ port: 0, channel: 0, pitch: 20, velocity 127
noteout _ port: 0, channel: 0, pitch: 16, velocity 0
noteout _ port: 0, channel: 0, pitch: 19, velocity 127
noteout _ port: 0, channel: 0, pitch: 21, velocity 0
noteout _ port: 0, channel: 0, pitch: 24, velocity 127
noteout _ port: 0, channel: 0, pitch: 20, velocity 0
noteout _ port: 0, channel: 0, pitch: 23, velocity 127
noteout _ port: 0, channel: 0, pitch: 19, velocity 0
noteout _ port: 0, channel: 0, pitch: 22, velocity 127
noteout _ port: 0, channel: 0, pitch: 24, velocity 0
noteout _ port: 0, channel: 0, pitch: 3, velocity 127
noteout _ port: 0, channel: 0, pitch: 23, velocity 0
noteout _ port: 0, channel: 0, pitch: 2, velocity 127
noteout _ port: 0, channel: 0, pitch: 22, velocity 0
noteout _ port: 0, channel: 0, pitch: 1, velocity 127
Underrun detected: 1 blocks dropped
Link to patch: