Yeah but doesn't the post count represent the number of available posts as opposed to the number of posts you haven't downloaded? If I run it again now it is consistently showing 651 posts, it doesn't download anything because they have already been fetched but the post count is wrong. It was the same before you changed the fetch order, only that time is was 1300 ish, these are now not being included in count.
So what I mean is there must be something in that boundary between the two counts that is causing it to stop fetching posts/counts.
I haven't done any C# for years now but I've got it running locally at least, Ill try and dig into it a bit.