I had an interesting glitch since this update: I send Sudoku PDFs via Send to Kindle. I happen to have 2 Scribes and when I downloaded one I'd marked up on the other, one of the pages lacked the solution I'd worked out on the first. Markup I made on the 2nd Kindle on the same page did sync back to the first.
I did manual sync on both devices, still those annotations did not show up on second Scribe.
Then I removed download on the first and re-downloaded it. The 'solution' was gone.
So somehow that entire page of pen annotations failed to get backed up to cloud, even though local file had them in there (until I removed the download).
Both should be more or less continuously able to connect to WiFi as I never use Airplane mode.
So in reference to @jhowell's findings in
post #9, there still seem to be some issues with syncing (at least of pen annotations).
It's been awhile since I experimented with sync between the two to see how well it worked, never saw any problems. Sync can be relatively slow (there's more data involved) but haven't seen it fail completely like this.
Of course it is troubling even if you only have one Scribe. How will you realize when some annotations haven't been backed up? You can view Notebooks and sticky notes with the Kindle app, but Print Replica pen annotations can only be viewed on Scribe.
Even if you can check it in theory, in practice the expectation is that annotations are backed up and in removing a download you cannot lose anything.