I probably solved it, but I don't understand that.
When I change the header of xsd schema from this one
<xs:schema xmlns:xs="https://www.w3.org/2001/XMLSchema"
targetNamespace="https://www.doctrine-project.org/schemas/orm/doctrine-mapping.xsd"
xmlns:orm="https://www.doctrine-project.org/schemas/orm/doctrine-mapping.xsd"
elementFormDefault="qualified">
to this one
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
targetNamespace="http://doctrine-project.org/schemas/orm/doctrine-mapping"
xmlns:orm="http://doctrine-project.org/schemas/orm/doctrine-mapping"
elementFormDefault="qualified">
xmlling begins to work as expected. So probably some https issue.
We will try to integrate xsd validation to our unit tests, so we can test all of 1000+ doctrine samples against xsd schema to ensure that everything is ok.
I will let you know.