php - Unexpected server error. when creating a shipping label in WooCommerce

As of 07/27/2021 I have just started to get the following error when trying to create a shipping label through WooCommerce:

"Unexpected server error"

I went to the WooCommerce Logs and found the following:

fatal-errors-2021-06-30-5a8cdf72b61eb062429327964e479de2.log

2021-06-30T21:13:42+00:00 CRITICAL Uncaught Error: Call to a member function get_instance_option_key() on bool in /var/www/wp-content/plugins/woocommerce/includes/class-wc-ajax.php:2900 Stack trace: #0 /var/www/wp-includes/class-wp-hook.php(292): WC_AJAX::shipping_zone_methods_save_changes('') #1 /var/www/wp-includes/class-wp-hook.php(316): WP_Hook->apply_filters('', Array) #2 /var/www/wp-includes/plugin.php(484): WP_Hook->do_action(Array) #3 /var/www/wp-admin/admin-ajax.php(187): do_action('wp_ajax_woocomm...') #4 {main} thrown in /var/www/wp-content/plugins/woocommerce/includes/class-wc-ajax.php on line 2900

All of my plugins are updated, and I was able to create shipping labels before 07/27/2021. Has anyone else had this problem, or know how to fix this please?

Solution:

Most likely a conflict with another plugin. Try disabling everything except for Woo and see if you still have the error. If you don't have the error start turning on plugins one by one until you find the one causing issues.