Hmm, I may not have a Mac, but it sounds like similar problems that I have had. Though Idk how I fixed it, if you do end up having to reinstall though, you can simply take out all of the map files including the particles, terrains, map files, cfgs, etc. and put them on your desktop then when you redownload the game, simply move everything back. If it ends up still having that problem after all of this, then it may be something to do with the maps. Hope this helped! ^^