Ever since we upgraded to CiviCRM 5.28.0, one of our sites is getting several error messages like this:
Notice: register_rest_route was called incorrectly. The REST API route definition for civicrm/v3/url is missing the required permission_callback argument. For REST API routes that are intended to be public, use __return_true as the permission callback. Please see Debugging in WordPress for more information. (This message was added in version 5.5.0.) in [site path]/wp-includes/functions.php on line 5225
There are eight error messages in total, all identical other than naming other civicrm/v3/* route names.
This is on WordPress. The core files and all plugins are at the latest versions, and the errors persist after we just updated to CiviCRM 5.28.3.
So far, Google has not revealed anything useful.
What might cause this problem?