iCloud sync for notes -- two different sets of notes on same account

Hi, I'm experiencing something very unusual. In short, some time last year, it looks like notes on an account, which are synced to iCloud, split: now, the notes synced to iPhone/iOS and iCloud.com are the same, but they are different from the notes synced to two different Macs (MBA and MBP). The two Macs show the same set of notes--which, again, is different from the set shown in iCloud and iOS.

I've tested disabling sync on the Macs, clearing the Notes containers, and disabling sync on the iPhone. Tried separately and concurrently in case that made a difference. In each case, when the notes are re-synced to iCloud, they continue on this divergent sync.

New changes made on one mac show on the other mac, but not iCloud.com or iPhone.

Changes made on iCloud.com/iPhone show on the other, but not the MacBooks.

100% these are the same iCloud account and the notes in the Notes app are the notes belonging to this iCloud account (indeed, no other accounts sync notes, plus I cleared cache/deleted the containers to force this). And, again, it's replicated on 2 devices.

So could this account really have two streams of Notes being synced? What can I do to get it to one across all devices (no need to merge)? Thanks.