Very often, when I make some annotations in a PDF file on DTTG, it never syncs to the sync store, (iCloudKit) so in DT3, I can’t see the changes made in DTTG.
So I tried to purge the PDF file that I annotated and re-download it on DTTG. What happened was that the annotations that I had just made were gone. So it is obvious that, at least with some PDFs, the changes made on DTTG are never uploaded to the sync store.