We use UltimateMember for our for our site membership needs. The Log Out option for UltimateMember directs users to https://mydomain.org/logout/?redirect_to=https://mydomain.org which logs the user out and returns them to the main page of the site.
If I put that URL into the Forum>>Components>>Login and Registration>>Log Out Redirect box, when I log out it takes me to the wp-login.php page. This leaves the WP login and registration page available to users, which we do not want to happen.
I also tried putting the URL in the Forum>>Components>>Login and Registration>>Alternate Logout URL box with the same results.
In fact, with either of those options defined (Log Out Redirect or Alternate Logout URL) even using the url itself to log out results in landing on the wp-login.php page.
If I leave the option blank, it logs me out but leaves me on the page I was on rather than taking me to the main page of the site.
I hope I am describing the issue clearly enough. 