Full of Fatal errors

From last 1 month my website was very slow.

Today I get response from server. Lots of error

PHP Fatal error:  Uncaught Error: Call to undefined function WPO\\WC\\PDF_Invoices\\list_files() in /woocommerce-pdf-invoices-packing-slips/includes/class-wcpdf-main.php:909

woocommerce-pdf-invoices-packing-slips/includes/class-wcpdf-main.php(882): WPO\\WC\\PDF_Invoices\\Main->temporary_files_cleanup(1662349171)\n#1 

php(138): do_action_ref_array('wp_scheduled_de...', Array)\n#5 {main}\n  thrown in /plugins/woocommerce-pdf-invoices-packing-slips/includes/class-wcpdf-main.php on line 909, referer:/wp-cron.php?doing_wp_cron=1662953971.6180651187896728515625

PHP Fatal error:  Uncaught Error: Call to undefined function WPO\\WC\\PDF_Invoices\\list_files() in /woocommerce-pdf-invoices-packing-slips/includes/class-wcpdf-main.php:909\n

Stack trace:\n#0 /woocommerce-pdf-invoices-packing-slips/includes/class-wcpdf-main.php(882): WPO\\WC\\PDF_Invoices\\Main->temporary_files_cleanup(1662262768)\n#1 

php(138): do_action_ref_array('wp_scheduled_de...', Array)\n#5 {main}\n  thrown in plugins/woocommerce-pdf-invoices-packing-slips/includes/class-wcpdf-main.php on line 909, referer: wp-cron.php?doing_wp_cron=1662867567.9611198902130126953125