​Empty fields are hidden on profile form "view" mode. It may look weird. You may use the code snippet below to display fallback value "--" for the empty fields. It works only for the "view" mode. Just add this code snippet to the functions.php file in the active theme (child theme) directory.

Display fallback value '--' if the field value is empty.php

<?php

/**
 * Displays fallback value if the field value is empty. For the "view" mode only.
 * @param  string $value
 * @param  string $default
 * @param  string $key
 * @param  string $type
 * @param  array  $data
 * @return string
 */
function um_field_value_fallback( $value, $default, $key, $type, $data ) {

	if ( empty( $value ) && isset( UM()->fields()->viewing ) && UM()->fields()->viewing === true ) {
		$fields_without_metakey = UM()->builtin()->get_fields_without_metakey();
		if ( !in_array( $type, $fields_without_metakey ) ) {
			$value = '--';
		}
	}

	return $value;
}
add_filter( 'um_field_value', 'um_field_value_fallback', 50, 5 );