When multiple notes are underlying a slash voice notehead, the music xml export includes all the backing notes. This causes trouble with import in Sibelius and Finale. I’ve attached an image of what Finale does. Sibelius is similar but no stems on the slash noteheads.
Don’t know much about finale. I send XML files of the piano/vocal to my music director so he can do the vocal arrangements. I don’t know much about the philosophy behind MusicXML, but if its intent is to capture what is displayed, then Dorico should be stripping the extra notes.