Created attachment 171015 [details]
document to examine page style
You might open attached document and resave it, e.g. to ODF 1.3 extended. The error is the same.
LibreOffice writes the element <style:graphic-properties> in a style of family page-properties. But that is not allowed there. Allowed is <style:drawing-page-properties>. The element is written because of the attribute draw:fill-hatch-solid. But this attribute may be used in element <style:drawing-page-properties> too. So there is not even a need for an extended namespace.
You can test the document with validator https://odfvalidator.org/.
The error exists already in LO 6.4. I wonder, that there is no report already.
I believe you and set to NEW