Troubleshooting after PHP 8.5 upgrade in WooCommerce

Troubleshooting after PHP 8.5 upgrade in WooCommerce

After a PHP 8.5 upgrade in WooCommerce, error messages, malfunctions and even failures such as the “White Screen of Death” often occur. The most important solutions are systematic debugging, targeted plugin checks and the adaptation of outdated code.

Typical errors after PHP 8.5 upgrade

The most common problems include:

• Fatal errors (E_ERROR) caused by deprecated functions such as create_function() .sprintf()
• “White page”: Usually caused by an incompatible theme or plugin.
• Deprecated notices as well as warnings in the backend, usually because of changed types or methods.
• Individual shop features (e.g. checkout, product pages) no longer work or provide errors.

Rapid immediate action

Activate WP_DEBUG: Set:

define('WP_DEBUG', true);
define('WP_DEBUG_LOG', true);
define('WP_DEBUG_DISPLAY', true);

in the wp-config.phpto get error outputs.

Update all plugins and themes: Install the latest versions of all WooCommerce plugins and your theme.

Deactivate and reactivate gradually: Disable all plugins and reactivate them individually to identify the faulty plugin.

Test theme switching: Temporarily enable a default theme (such as Twenty Twenty-Five) to rule out theme issues.

Common source of error: Unmaintained or outdated code

The function create_function() is removed as of PHP 8.x. If it is used in child themes or plugins, it must be replaced with function () { ... }.

The constructor of widgets has changed: Replace:

function meineklasse() {
    WP_Widget::construct(...);
}

through:

function __construct() {
    parent::__construct(...);
}

Check all in-house developments, snippets and code extensions for outdated methods.

Concrete WooCommerce error message: “Missing format specifier in sprintf”

A common mistake is:

textUncaught ValueError: Missing format specifier at end of string in .../class-wc-post-types.php

Solution:

• Update to the latest WooCommerce version.
• If the error persists, check if another plugin accesses the function or overwrites the file.
• In an emergency, temporarily reset the PHP version until a patch is available.

Increasing the PHP Memory Limit

Sometimes even increasing the memory limit helps:
To do this, paste into the wp-config.php following line:

phpdefine('WP_MEMORY_LIMIT', '256M');

Important: The command must precede the closing PHP tag.

Troubleshooting blocked backend

If you can’t get to the backend at all:

• Disable plugins manually via FTP or in the database.
• For premium plugins: Check for updates or contact support directly with your bug report and debug log.

Long-term strategy

• For all main plugins (especially WooCommerce, payment gateways), rely on actively maintained products with official PHP 8 support.
• Consider changing the theme if there are problems with the previous theme and no update is available.
• Be sure to disable the debug tools after the error analysis to avoid security risks.

With this process, you can analyze and fix most of the typical errors after a PHP 8.5 upgrade in WooCommerce – both for customer projects and for your own shops.