wp-admin redirect loop with custom login page and ssl enabled

please considure WordPress config bellow
define('FORCE_SSL_ADMIN', true);
and htaccess

###Force https
RewriteCond %{HTTP:X-Forwarded-Proto} !https
RewriteCond %{HTTPS} !=on
RewriteRule ^(.*) https://%{SERVER_NAME}/$1 [L,R=301]
###Force https Ends

###WordPress Seo Settings
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ - [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>
###WordPress Seo Settings Ends

it was working pretty well. but after adding a custom login page in WordPress, wp-admin encountered with redirect loop. after hours of debugging we found that the redirecting loop ends if we disable the ssl (also custom login page works well) or remove the custom login page.
i already tried to fix the file permission and file owner in server by ssh but it won’t work.
please reply if anyone have any kind of fix for this.