I found that the mod-security is triggering because these pages have a content something like “blacklist_keys”. (Its a false detection)
The fix is to replace this word with some other words like “simple_keys” in the given below files.
wordpress directory/wp-admin/includes/schema.php
wordpress directory/wp-admin/options-discussion.php
wordpress directory/wp-admin/options.php
or remove the lines which are having “blacklist_keys” in these two files.
wordpress directory/wp-admin/includes/schema.php
wordpress directory/wp-admin/options-discussion.php
then remove only the “blacklist_keys” from the file.
wordpress directory/wp-admin/options.php
