Lightroom 13.3.1 SDK sync: local changes to title/caption are reverted by sync back from cloud

(Mac OS 14.5, LRC 13.3.1)

I am using a SDK plug-in to modify title and caption (title from my iNaturalist collection, and caption from my Strava logs, plus GPS from Strava and keywords to document what changed).
Up until yesterday (previous version), it worked great.
Today after update to 13.3.1, I updated a bunch of changes to my library; the keywords and GPS lat/lon all stuck, but the title and caption changes all spontaneously reverted in about 5 minutes.

I paused syncing, and reran the update.
The title can caption changes stuck while syncing was paused.

I unpaused syncing, and all the title/caption changes reverted back once again within a few minutes.
I have never seen the modified title/caption appear in the synced cloud copy. It's like it doesn't recognize it as a new change.

Note that if I change the title and caption manually, everything works as normal; obviously updates through the UI are triggering a push as they should.

 

Note also, it's not some change context reverting it locally; if I exit Lightroom immediately after making the changes, and restart it after 5 or 10 minutes, the changes are still there and stick for about 5 minutes, then they revert again (if syncing is on, not if paused).

I connect this with LRC 13.3 update "sync performance updates". I suspect a bug.

Is there some new (perhaps hidden) API call to propagate title and caption changes?
Has anyone else seen spontaneous reversion of anything back from the cloud?