Edited: This problem has now been resolved.
There is currently a known issue on Connect that is causing some groups to not appear on the site. We believe that we have isolated the problem and are currently working to restore access to these groups. Rest assured that there were no security threats with this action. In addition, we do not believe that any content in these groups will be lost. It is an internal server issue. We do not have an estimated time that these groups will be restored, but do not anticipate that it will be a long-term problem. We will update this blog when we do have a time to resolution.
If you have any questions, please feel free to contact Leslie Miller.