Reply To: An error of type E_ERROR was caused in line 503 … Unsupported operand types

Unfortunately the error has recurred, although the Error Details provided by WordPress are different, viz.

Error Details
=============
An error of type E_ERROR was caused in line 503 of the file /home/’username’/public_html/wp-content/plugins/responsive-lightbox/includes/class-frontend.php. Error message: Uncaught Error: Unsupported operand types in /home/’username’/public_html/wp-content/plugins/responsive-lightbox/includes/class-frontend.php:503
Stack trace:
#0 /home/’username’/public_html/wp-content/plugins/responsive-lightbox/includes/class-galleries.php(3806): Responsive_Lightbox_Frontend->get_unique_fields(Array, NULL)
#1 /home/’username’/public_html/wp-content/plugins/responsive-lightbox/includes/class-galleries.php(4153): Responsive_Lightbox_Galleries->save_gallery(Array, 2661, true)
#2 /home/’username’/public_html/wp-includes/class-wp-hook.php(287): Responsive_Lightbox_Galleries->save_revision(2661)
#3 /home/’username’/public_html/wp-includes/class-wp-hook.php(311): WP_Hook->apply_filters(”, Array)
#4 /home/’username’/public_html/wp-includes/plugin.php(484): WP_Hook->do_action(Array)
#5 /home/’username’/public_html/wp-includes/revision.php(347): do_action(‘_wp_put_post_re…’, 2661)
#6 /home/’username’/public_html/wp-admin/includes/post.php(1874): _wp_put_post_revision(Array, true)
#7 /home/’username’/public_html/wp-a

WordPress version 5.6.2
Current theme: Twenty Sixteen (version 2.3)
Current plugin: Responsive Lightbox & Gallery (version 2.3.2)
PHP version 7.4.14

Can anyone help please?