In the StructureDefinition of unsignedInt and positiveInt, the type of the value element is http://hl7.org/fhirpath/System.String but should be http://hl7.org/fhirpath/System.Integer.

Please see the discussions here: https://chat.fhir.org/#narrow/stream/179166-implementers/topic/unsignedInt.20and.20positiveInt.20string.20in.20JSON.20and.20FHIRPath.3F and here: https://chat.fhir.org/#narrow/stream/179177-conformance/topic/Int.20type.20question.20in.20R4.20StructureDef