I have not created a new RM file from Treeshare for ages and I have never used a Mac, but I have seen lots of examples of Treeshare missing data from Ancestry. See my long series of posts here (there are actually other posts in other threads) and recent comment on this thread.
All these problems seem to have a common theme, information going missing between Ancestry and Treeshare apparently at random. As I have noted in my posts, I see three possibilities. 1) Ancestry may not be sending the complete data, 2) the data may be getting lost between Ancestry and Treeshare and the communications protocol may not be robust enough to detect and rectify this or 3) Treeshare may for some unknown reason be failing to process all the data it receives.
As to your specific question, to have Ancestry resend data on any person, just force a change in their profile. I generally add a letter to the detail of a birth record or whatever and then delete it again. This person should then show up in Treeshare.
I always check that I end up with the same number of people in the two sides.