There is a declared rule in the Schematron expression cva/UBL-DocumentConstraints-2.3.pattern.sch that is missing a required child to be Schematron schema-valid. This can be satisfied with a simple <report test="false()"/>

Repairing this has no impact on execution nor is the fault translated to the generated val/UBL-DefaultDTQ-2.3.xsl used for validation.

Where users might find a problem is if they incorporate the UBL pattern into their own Schematron schemas and then try to validate the schema ... they will get a validation error.