Sorry about the delay in replying. I wanted to do some testing before replying. I believe I know where the problem lies.
I imported a brand new sample 1 page pdf into DTTG, and went through several cycles of annotating it in PDF Expert iOS, syncing DTTG and DT Pro Office (using Dropbox sync), annotating the same file on PDF Expert desktop version, re-syncing and checking the file on DTTG. Even after several cycles of this, all annotations showed up appropriately.
However, I then annotated the file on DTTG itself and closed it. I then opened the file on PDF Expert iOS but it did not show the DTTG annotation. I annotated the file on PDF Expert - when I reopened the file on DTTG it showed the most recent DTTG annotations, but not the PDF Expert annotations. From that point on, syncing the file and opening it on the DT Pro Office would only reflect the post-DTTG-annotation version of the file.
Long story short, it appears that annotating a file in DTTG creates a new version of the file. This new version is viewable and editable within the DT iOS and desktop framework, but is no longer present within the iOS Document Provider framework or available to any other iOS applications.
Appreciate your thoughts on the issue. Thank you.