To reproduce, create a space "TestBug" in Confluence, then do the following on the space permissions:

1. Strip out all Anonymous access from TestBug
2. Remove the jira-administrators group from group permissions (note we are using integrated access from JIRA)
3. Add in admin-user1 to the individual users section
4. Login as admin-user2
5. Confirm that admin-user2 is unable to see TestBug space in list of spaces
6. Go to Confluence Admin -> Space Permissions
7. Press the "Recover Permissions" button for TestBug
8. It should change to "Manage Permissions"; try to click that link
9. You should get to an error page saying Not Permitted

Now, back as admin-user1, you can validate that admin-user2 got added to the individual users section as an Admin, but has no View access, so cannot see the admin page.

This is bad news if you dont have a fellow admin to help you unlock yourself or regain access.