The plugin uses transients to store the user queries to speed up the listing page. And in theory, it’s supposed to clear these transients out at various times when user-related actions happen.
add_action( 'profile_update', array( $this, 'delete_user_transients' ) );
add_action( 'user_register', array( $this, 'delete_user_transients' ) );
add_action( 'delete_user', array( $this, 'delete_user_transients' ) );
add_action( 'save_post', array( $this, 'delete_user_transients' ) );
That should include when you register a new user. I don’t know what would be preventing that from happening. Is it multisite? Do you have anything in your error logs? Are you on a host with extensive caching? Any caching plugins? There are a lot of things you should check.
Also, try disabling other plugins, then save/update a user. That is supposed to also clear the transients. If nothing is working, you can use a plugin like Transients Manager to delete any transient with sul_query
in it.