We aren't aware of any general issues with the use of AstroPosition. As indicated in the previous response, AstroPosition has to download ephemeris files in order to perform this calculation (~83 MB for this query I believe).
Notice the last item in the Details in the ref page for AstroPosition:
AstroPosition downloads ephemeris data files for solar system objects, storing them permanently in
FileNameJoin[{$UserAddOnsDirectory,"ApplicationData","Astro"}]
If your system doesn't have permissions, not enough hard drive space, etc then perhaps there might be some kind of issue, but this is not a general issue. Its likely specific to your system.
I'm not a Mac user so can't speak to what Mac specific issues may or may not be responsible for your difficulties.
Feel free to comment on your configuration here, but such questions are likely more appropriate for a query to support@wolfram.com
