Custom backend redirect url does not work anymore

Hi all,

i use ithemes security plugins in 6 of my WP sites. After updating WP to 4.6.1, latest theme and plugins, i found that in only one (!!!) of my sites that use the ithemes security plugin, the admin redirect url does not work anymore.

First things first. I remember there was a choice to modify the /wp-admin/ url to some other, so i changed this to /my-admin-panel/, but i cannot find this option anymore from the plugin settings.

Now, all my sites still work with /my-admin-panel/ except from the one site mentioned that the /my-admin-panel/ no longer redirects me to the admin panel (/wp-admin), instead it redirects me to the frontend as a visitor (no login form is displayed). In order to login i have to type /wp-login.php (please notice that /wp-login does not work either).

So my questions are:
1) What has changed to ithemes security and backend redirect custom url does not exist anymore?
2) Why only one of my 6 sites is affected and can no longer login via custom url?
3) Why does it login via /wp-login.php and not via /wp-login?

thanks in advance