OK, I'm back home today on my reasonably super-duper system.

First, yes, your description of Thelonius Monk is just right to describe the first beat. And that's not a compliment to Monk; I always wondered a bit when I heard his playing. The second beat, I might describe as someone falling down the stairs while playing.

Now, why?

The first thing I see is that you call have been discussing triplets, but the Microchords dialog does not show that. The Chordsheet shows E9,,F9. Note the two commas. This sets up a triplet with the missing middle note.

I didn't yet listen to what you are trying to accomplish, and whether it is supposed to be Swing feel. Give me some time later.

Interestingly, Bar 17 does sound like triplets, but you didn't enter any chords there. I have no idea why that one worked, at least to my ear. Perhaps the program saw the attempted rhythm in bar 16, and although it played that spastically, it "got the idea" to do something similar in bar 17 comping, and got it right. We users can only guess at that one.

Fun little project.

BIAB 2025 Win Audiophile. Software: Studio One 7 Pro, Swam horns, Acoustica-7, Notion 6, Song Master Pro, Win 11 Home. Hardware: Intel i9, 32 Gb; Roland Integra-7, Presonus 192 & Faderport 8, Royer 121, Adam Sub8 & Neumann 120 monitors.