A couple of more things that may be relevant. I am using a customized skeleton.php plugin on the site, along with mailonchangefield.php to capture notifications when users change their email address. If you need to see these files, please see the attached.

These have not been changed in over 18 months, but maybe other changes made to EasyProfile affect how this code currently is written and behaves. Is there a better way of managing this?

Thanks in advance.

Hi,
Error
This alert was added because in many sites there are many routing problem.

When you have "registration" menu item but missing "edit profile" (or "profile" menu item the Joomla routing not works well (read here more info https://www.easy-profile.com/support/404-when-user-updates-his-profile.html#reply-8835)

If you have not problem then you can ignore this message, anyway to remove it you can simply search in your menu section all menu items of type "Users->Registration Form" and set Access to Guest. Already registered users do not need to see this menu item.

Plugins
Easy Profile event system is the same also in latest version, so you should not have problem due to update. To keep consistency with the email addresses I can suggest an excellent free plugin called "Email Activation" (http://extensions.joomla.org/extension/email-activation), this plugin allow users to confirm new email address before set changes.