Grab https://github.com/HiraokaHyperTools/SampleXpsDocuments_1_0/raw/refs/heads/master/Handcrafted/GradientStops.xps and issue
$ xpstopdf GradientStops.xps GradientStops.xps.pdf
Error rendering page 1: Error rendering page /Documents/1/Pages/1.fpage: /Documents/1/Pages/1.fpage:13:59 missing attribute 'Offset' of element 'GradientStop'
$ mupdf GradientStops.xps &
$ mupdf GradientStops.xps.pdf &
Observe that the squares are lost. In the screenshot in the attachment, the left document is the original XPS, and the right one is the converted one.