If I follow a process I mentioned here, I am supposed to log out and then in for the changes to take place. What about Nautilus? I tried to restart it and was still unsuccessful. The only way I have so far found that works is logging out of the desktop and then in again. That's not always convenient of course.
You can't grant a new group to a running process. You need to log in again to get a process with the changed group memberships.
What you can do is to launch nautilus from a different session but have it display on your existing display, something like