Display name filled with username instead of first name and last name

Hi —

I read in another post for your plugin that:
“The display name is always set to the user’s first and last name, or username if first and last name fields are empty, it cannot be updated for a user’s profile through a form field.”

We are not having that experience. Even though the first and last name fields are filled in upon registration, the display name is being set to username. We would like to set the display name to first and last name. Is there a function that we can add to do that?

Thanks,
Kari