There is a reload button in the group detail. That should reload it manually. Note that you need to open the nested toggle, the one to the left of the file path.
Are you using the Mac App store version? There is an issue with the sandbox, in that you need to have read access to the folder that the file is in, not just the file. When you hit the Reload button you will get a message telling you to go to the preferences settings and add read access to the folder.
Regarding the lost link issue: Was the column type not a number already? The link is dynamic and in fact the data is not stored in the file which means that it won’t take up space but also means that if the file goes away the column will be empty.