I recently joined a group but after joining, I noticed that the group was not listed in my Groups tab. Since the group is not listed there, I am unable to select this group and leave this group.
I investigated how this was possible. My profile still listed me as a member of this group and when I go to the group properties (using search or profile) it still lists (and recognize) me as a member. However, as said, it is not listed in my Groups tab. I experimented with my own group and found out that when an avatar is assigned to a role that has no abilities (all abilities are unchecked), the group is no longer listed in the group tab of avatars that are assigned to this "no ability role".
Here is how you can test:
1. Go to a group (or create one) and make sure to add an avatar to the "Everyone" role. (this avatar is not assigned any other role)
2. Remove all allowed abilities of the "Everyone" role.
3. Login as the avatar that has been assigned to the "Everyone" role.
4. Confirm that the group is not listed in the Groups tab.
5. Confirm that the avatar is still a member of the group by looking at the profile.
(if this example works as expected, contact me, and I"ll assign you to a role in my group to see if you can leave it.)
I confirmed this with version 1.19.1 and 1.20RC4 of the viewer.