EZP-23644 introduced changes in the schema.xml file related to multiple locations and hidden objects.

With a composer update, the changes will be made in "ezp-default/conf/schema.xml" but since this specific change is not pointed in eZP 5.3.5 Release notes the customer might miss that steps and the upgrade will fail.

It's important to change that page indicating you must propagate schema.xml changes to all the schema.xml files.