Creates Soft 404 Errors

This is the incorrect way to handle a 404. You can specify a custom 404 page right in your .htaccess file. It’s nice that there is a plugin for those that don’t want to or don’t know how to manage a .htaccess file, but this plugin does it in the wrong way.

The problem is it forwards the visitor to your “404” page, but the status code it gives is 200. So if old pages are indexed in Google, even though you are taking them to your custom 404 page, you’re telling Google that the original page actually exists. It’s inconsistent. It needs to give a 404 status.

https://support.google.com/webmasters/answer/2409443/?ctx=MCE&ctx=S4&hl=en&authuser=1