All in One SEO on PHP 8.6: deprecation notices and the fix

On PHP 8.6 (due 19 November 2026), All in One SEO 5.0.4 logs a deprecation notice on every ordinary page load in our test. We found 4 places in its code that PHP 8.6 flags. Nothing stops working; the notices go to your PHP error log and show on pages where errors are displayed.

Tested on 28 October 2026 with the official PHP 8.6.0RC4 build and WordPress 7.1.1, plugin version 5.0.4 (2,000,000+ active installs) from WordPress.org, activated alone with default settings.

The messages you will see

Deprecated: Returning a value from a constructor is deprecated

Deprecated: Calling is_a() with a string when $allow_string is false

Where they come from

File:line	What	When PHP 8.6 complains	In our WordPress test
`app/Common/Models/Model.php:144`	returns a value from a constructor	Compile time: logged when PHP loads the file	on every front-end page load
`app/Common/Models/Model.php:147`	returns a value from a constructor	Compile time: logged when PHP loads the file	on every front-end page load
`app/Common/Models/Model.php:150`	returns a value from a constructor	Compile time: logged when PHP loads the file	on every front-end page load
`app/Common/Traits/Helpers/WpContext.php:249`	calls `is_a()` with a string	Seen in our test	in wp-admin

The fix

Site owners: you don't need to change anything to keep the site working. Keep display_errors off on the live site, and update All in One SEO when a release mentions PHP 8.6. If a notice shows on your pages, set define( 'WP_DEBUG_DISPLAY', false ); in wp-config.php.

Plugin developers, line by line:

returns a value from a constructor: Change return …; inside __construct() to a bare return;. new always returns the object, so the value was never used.
calls is_a() with a string: Use $value instanceof ClassName, or pass true as the third argument if strings are meant to be accepted. PHP 8.6 complains whenever is_a() gets a string while $allow_string is false.

What a PHP 8.6 deprecation notice does, and what it doesn't

Nothing stops working on PHP 8.6. A deprecation is a warning that the code will break in a future major version (PHP 9, no date yet). The plugin keeps working.
It lands in your logs. With log_errors on (the usual hosting default) every notice goes to the PHP error log, and with WP_DEBUG_LOG to wp-content/debug.log.
It can show on the page. If display_errors is on, or WP_DEBUG is on without WP_DEBUG_DISPLAY set to false, the notice is printed into the page. That breaks AJAX/JSON responses and can cause "headers already sent" warnings. Keep display off on live sites.
Compile-time notices are logged when PHP compiles the file. With OPcache that happens once after a restart or cache reset, so you see a few lines, not one per visit. Function notices (spl_object_hash(), is_integer()…) are logged every time that code runs.

All 39 affected plugins out of the 100 most popular, and the 61 with no findings: PHP 8.6 and WordPress plugins.

Sources

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