Issue :
I get this warning on one of my self-hosted WordPress site and this shows only in the admin area.
Warning: Illegal offset type in /home/mydirectory/public_html/mydomain.com/wp-admin/includes/template.php on line 1135
Solution :
In my case, the issue was due to the WordPress plugin called “WP Database Backup“. After i deactivated this plugin, my issue solved.