Cannot Edit User's Role

I am trying to edit a user’s Role.

If select a different role from the drop-down menu (when editing a user), I then click “Update User” at the bottom… the setting does not “stick”.
When I reload the user, the Role is still in the original one.

When I de-activate iThemes Security, if i perform this edit again, the User’s Role changes as expected.

Any idea what could be going on?
Maybe I changed a setting on iThemese Security I shouldn’t have changed?

I have installed s2Member, for providing different “membership levels” to this site.

All help is grately appreciated!
Please let me know any additional information that could help with troubleshooting.

Thank you!

https://wordpress.org/plugins/better-wp-security/