As described in detail here: drewnoakes/metadata-extractor-dotnet#418 by @Numpsy and confirmed by @kwhopper, it seems like there's a bug from the java import of xmp-core-dotnet, where, if rdf namespace definition is attached to the <x:xmpmeta node (correct behaviour as per C++ version of XMP-toolkit-sdk) rather than the rdf:RDF node (the way xmp-core-dotnet expects it but is incorrect behaviour), xmp-core-dotnet throws an error