Version 3.6.0 introduced the folder /includes/Compatibility while the files are stored in /includes/compatibility, but there appear to be ways to update sites where the folder with the uppercase letter was created first and the files ended up in that folder instead of the lowercase folder. They are used from the folder with the lower case folder, so it gives errors as code cannot be loaded.
This resulted in the following errors:
PHP Warning: include(/.../wp-content/plugins/woocommerce-pdf-invoices-packing-slips/vendor/composer/../../includes/compatibility/class-wcpdf-compatibility-third-party-plugins.php): Failed to open stream: No such file or directory in /.../wp-content/plugins/woocommerce-pdf-invoices-packing-slips/vendor/composer/ClassLoader.php on line 582
PHP Warning: include(): Failed opening '/.../wp-content/plugins/woocommerce-pdf-invoices-packing-slips/vendor/composer/../../includes/compatibility/class-wcpdf-compatibility-third-party-plugins.php' for inclusion (include_path=".:/opt/alt/php81/usr/share/pear:/opt/alt/php81/usr/share/php:/usr/share/pear:/usr/share/php") in /.../wp-content/plugins/woocommerce-pdf-invoices-packing-slips/vendor/composer/ClassLoader.php on line 582
PHP Fatal error: Uncaught Error: Class "WPO\WC\PDF_Invoices\Compatibility\Third_Party_Plugins" not found in /.../wp-content/plugins/woocommerce-pdf-invoices-packing-slips/woocommerce-pdf-invoices-packingslips.php:195
Stack trace:
#0 /.../wp-content/plugins/woocommerce-pdf-invoices-packing-slips/woocommerce-pdf-invoices-packingslips.php(239): WPO_WCPDF->includes()
#1 /.../wp-includes/class-wp-hook.php(310): WPO_WCPDF->load_classes()
#2 /.../wp-includes/class-wp-hook.php(334): WP_Hook->apply_filters()
#3 /.../wp-includes/plugin.php(517): WP_Hook->do_action()
#4 /.../wp-settings.php(495): do_action()
#5 /.../wp-config.php(99): require_once('/.../...')
#6 /.../wp-load.php(50): require_once('/.../...')
#7 /.../wp-blog-header.php(13): require_once('/.../...')
#8 /.../index.php(17): require('/.../...')
#9 {main}
thrown in /.../wp-content/plugins/woocommerce-pdf-invoices-packing-slips/woocommerce-pdf-invoices-packingslips.php on line 195The folder is currently present in both the 3.6.0 and 3.6.1 tags and in trunk.
For reference: this site was hosted at Neostrada (cPanel) and had automatic updates enabled. I don’t know the history of the updates, because I’m not the regular maintenance guy and was only hired to fix the shop that was offline most of the day because of this.