The problem's origin is not directly related to any 3rd party plugin, but rather to a custom code. The error occurs in the Wordpress core function _wp_filter_build_unique_id
: https://github.com/WordPress/WordPress/blob/master/wp-includes/plugin.php#L989
_wp_filter_build_unique_id
is used when modifying filters so the cause may be found in eg. add_filter()
, has_filter()
or remove_filter()
.
The problem can be mitigated by adding an isset()
check but is not advisable. Rather, the root cause for the problem should be fixed.
Wordpress version used: 6.6.1
Disabling plugins didn't make the error disappear, reverting to default theme (Twenty-twenty-one in this case) did.
The problem was calling add_filter() in a wrong way by not passing the second argument as string.
Fixed by changing add_filter('woocommerce_show_page_title', __return_null())
to add_filter('woocommerce_show_page_title', '__return_null')