So what you are saying is that you see this blue text below on the htaccess File Editor page correct? If so, then the Root htaccess is actually locked and the problem you are describing is something on your website or server is preventing the Turn On AutoLock POST Form from processing the Form code/submit. You can try deactivating all of your other plugins and see if the Turn On AutoLock Form works. If you have Mod Security enabled then a Mod Security SecRule or SecFilter could be preventing the Turn On AutoLock Form from working.
Your root htaccess file is Locked with Read Only Permissions.
Use the Lock and Unlock buttons below to Lock or Unlock your root htaccess file for editing.