This plugin shows many php notices/warning (on php 7.3 with notices/warnings enabled):
on /wp-admin/edit.php?post_type=shop_order
Warning in_array() expects parameter 2 to be array, null given
wp-content/plugins/additional-order-filters-for-woocommerce/additionalorderfilters.php:248
Notice Undefined variable: output
wp-content/plugins/additional-order-filters-for-woocommerce/additionalorderfilters.php:230
Notice Undefined variable: opened
wp-content/plugins/additional-order-filters-for-woocommerce/additionalorderfilters.php:234
Notice Undefined index: post_status
wp-content/plugins/additional-order-filters-for-woocommerce/additionalorderfilters.php:246
on /wp-admin/edit.php?post_status=wc-completed&post_type=shop_order
Warning count(): Parameter must be an array or an object that implements Countable
wp-content/plugins/additional-order-filters-for-woocommerce/additionalorderfilters.php:401
Warning Invalid argument supplied for foreach()
wp-content/plugins/additional-order-filters-for-woocommerce/additionalorderfilters.php:402
Warning in_array() expects parameter 2 to be array, string given
wp-content/plugins/additional-order-filters-for-woocommerce/additionalorderfilters.php:248
Notice Undefined variable: output
wp-content/plugins/additional-order-filters-for-woocommerce/additionalorderfilters.php:230
Those warnings/notices comes mainly because $_GET[‘post_type’] doesn’t exist or not an array if you click on the status filters of woocommerce itself
