I empathize. The words I hate to hear most “It worked for me”
I just reset a site on a subdomain using my steps above. One further step was that I made sure the .htaccess file was 100% default using the code in following link.
https://codex.www.ads-software.com/htaccess
I did search PHPMyAdmin for the custom login URL that I used via another plugin but in this site it appeared that the rewrite rule was still left in the .htaccess file. Sometimes deactivating a plugin and deleting doesn’t really delete it all.
Results on a site on a subdomain
The hide backend on the site on a subdomain appears to be functioning normally.
Couple of things of note:
– if you change the HIDE BACKEND slug I did not use a trailing slash. I thought I did and when I typed the login URL with the trailing slash….dumb mistake…I thought things were still broken but just mistyped. The ID-Ten-T error.
– if a site still gave me problems I did the above steps again. Perhaps I missed something….perhaps it had to be “convinced”. The second time around worked.
Ever since 4.0.2 the hide backend feature did not work. Errors, blank login page, 403 and 404 errors on logging out if the plugin, but not hide backend, was active.
4.0.23 with the steps mentioned in both my posts appears to have worked…for me. YMMV.
I hope this helps.
WP 3.8.3
iThemes 4.0.23
Shared webhost – successful on two different shared webhosts.