No dice, let 20 tracks sit for almost two weeks in the original folder with no SA data generated (about ~730 tracks in the original album at that point). Moved it back to _A and it populates (that folder is ~400 tracks).
There’s some kind of limit where the SA generation tops out at somewhere past 700.
I suppose i’ll keep adding to _A and merge once i’ve filled it up and start a _B folder.
Still looking for help solving this, since at one point this whole album (+2K) had SA data before I regrettably decided to do the plex dance.