Yes, exactly the same issue. Difficult thing is that Mendix does not provide a convenient way to check why the import mapping-operation fails: it just returns an empty object.
Got it sort of working now. Mendix is really picky on the XSD file, if the structure there is incorrect, then it doesn't work. Tried many different XML to XSD converters online, and now found one of them that works sort of: https://xmlgrid.net/xml2xsd.html
But still a head ache to find out why certain values/attributes are not imported correctly.
Did you ever find a solution for this problem?