Workaround:
If you mark out line 6 in header.php it works.

/**$avia_config[‘use_standard_lightbox’] = empty( avia_get_option( ‘lightbox_active’ ) ) || ( ‘lightbox_active’ == avia_get_option( ‘lightbox_active’ ) ) ? ‘lightbox_active’ : ‘disabled’;

* Allow to overwrite the option setting for using the standard lightbox
* Make sure to return ‘disabled’ to deactivate the standard lightbox – all checks are done against this string
*
* @added_by Günter
* @since 4.2.6
* @param string $use_standard_lightbox ‘lightbox_active’ | ‘disabled’
* @return string ‘lightbox_active’ | ‘disabled’
*/
$avia_config[‘use_standard_lightbox’] = apply_filters( ‘avf_use_standard_lightbox’, $avia_config[‘use_standard_lightbox’] );