When you say "folder" do you mean the grid or are you talking about selecting a folder in the Folder Panel? Either way, this is usually only a random problem for which I have never seen a solution. The only tip I can give you (on Windows) is to use the Home and End keys to move to the first or last image in the view. I don't know whether it will help but you can also try going to File>Manage Catalogs and using the Repair and Optimize options on your catalog.