“Critical error” message with v3.40.0 (but site seems fine)

This happened on just two of my five sites today when updating to the latest version. In both instances, the site came back immediately upon refresh, and everything seems fine both on the sites and in the WP Dashboards. Still, thought I’d share in case you need to know.

It seems the way I triggered the issue was, once the update finished, I refreshed the page (the wp-admin/update-core.php page), then hit “Flush Cache” from the “Managed WordPress” dropdown. That triggered the white screen with the “critical error” message and the email. I refreshed again, and the page came back and all seems fine again.

FYI:

An error of type E_ERROR was caused in line 226 of the file /var/www/wp-content/plugins/ml-slider/admin/Notices.php. Error message: Uncaught TypeError: array_merge_recursive(): Argument #2 must be of type array, null given in /var/www/wp-content/plugins/ml-slider/admin/Notices.php:226

Stack trace:

#0 /var/www/wp-content/plugins/ml-slider/admin/Notices.php(226): array_merge_recursive(Array, NULL)

#1 /var/www/wp-content/plugins/ml-slider/admin/Notices.php(293): MetaSlider_Notices->seasonal_notices()

#2 /var/www/wp-content/plugins/ml-slider/admin/Notices.php(145): MetaSlider_Notices->valid_seasonal_notices()

#3 /var/www/wp-content/plugins/ml-slider/admin/Notices.php(48): MetaSlider_Notices->lite_notices()

#4 /var/www/wp-content/plugins/ml-slider/admin/Pages.php(40): MetaSlider_Notices->__construct(Object(MetaSliderPlugin))

#5 /var/www/wp-content/plugins/ml-slider/ml-slider.php(132): MetaSlider_Admin_Pages->__construct(Object(MetaSliderPlugin))

#6 /var/www/wp-includes/class-wp-hook.php(310): MetaSliderPlugin->setup('')

#7 /var/www/wp-includes/class-wp-hook.php(334): WP_Hook->apply_filters(Object(MonsterInsights_Lite), Array)

#8 /var/www/wp-includes/plugin.php(517): WP_Hook->do_action(Array)

#9 /var/www/wp-settings.php(495): do_action('plugins_loaded')

#10 /var/www/wp-config.php(103): require_once('/var/www/wp-set...')

#11 /var/www/wp-load.php(50): require_once('/var/www/wp-con...')

#12 /var/www/wp-admin/admin.php(34): require_once('/var/www/wp-loa...')

#13 /var/www/wp-admin/update-core.php(10): require_once('/var/www/wp-adm...')

#14 {main}

  thrown

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