PHP Fatal Error

This just started appearing in the last two days:

[06-Feb-2019 00:16:23 UTC] PHP Fatal error:  Uncaught Error: Call to undefined function is_410() in /home/stcwdc57/public_html/events.stcwdc.org/wp-content/themes/aaron-child/410.php:18
Stack trace:
#0 /home/stcwdc57/public_html/events.stcwdc.org/wp-includes/template.php(688): require_once()
#1 /home/stcwdc57/public_html/events.stcwdc.org/wp-includes/template.php(647): load_template('/home/stcwdc57/...', true)
#2 /home/stcwdc57/public_html/events.stcwdc.org/wp-content/plugins/wp-410/wp-410.php(366): locate_template('410.php', true)
#3 /home/stcwdc57/public_html/events.stcwdc.org/wp-includes/class-wp-hook.php(286): WP_410->check_for_410('')
#4 /home/stcwdc57/public_html/events.stcwdc.org/wp-includes/class-wp-hook.php(310): WP_Hook->apply_filters(NULL, Array)
#5 /home/stcwdc57/public_html/events.stcwdc.org/wp-includes/plugin.php(453): WP_Hook->do_action(Array)
#6 /home/stcwdc57/public_html/events.stcwdc.org/wp-includes/template-loader.php(12): do_action('template_redire...')
#7 /home/stcwdc57/public_html/events.stcwdc.org/wp-blog-header.php(19): require_o in /home/stcwdc57/public_html/events.stcwdc.org/wp-content/themes/aaron-child/410.php on line 18

Hasn’t happened before now. What has changed? The code on Line 18 in the child theme’s 410.php is:

				//If we are viewing a post or page, and we want to combine it with the header section.
				if ( is_singular() && aaron_get_meta( 'aaron_show_header' ) || is_home() && aaron_get_meta( 'aaron_show_header' ) || is_single() && aaron_get_meta( 'aaron_show_header' ) || is_page() && aaron_get_meta( 'aaron_show_header' ) || is_archive() && aaron_get_meta( 'aaron_show_header' ) || is_search() && aaron_get_meta( 'aaron_show_header' ) || is_page_template() && aaron_get_meta( 'aaron_show_header' ) || is_410() && aaron_get_meta( 'aaron_show_header' ) && !is_front_page() ) {
							the_title( '<h1 class="site-title" itemprop="headline">', '</h1>' );
						}

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