I tried again today at 12:32 a.m. ET (New York) I entered https://gnusocial.net/group/gnusocial as the field to join remote group I was given the option to confirm joining remote group, when I did I get error "Remote group join failed!"

FYI gnusocial.jp is a social network, courtesy of GNU social JP. It runs on GNU social, version 2.0.1-beta0, available under the GNU Affero General Public License.