I had an issue yesterday which I was able to solve but, at the time, couldn't see any help articles with this answer (Mac & iPhone). The problem was I hadn't used XD for a while and when I went to device preview my recent design I was only able to see a really old design that wasn't even on my computer anymore. It was loaded fully but wasn't the file I had open on my desktop. I read about deleting offline docs, I also tried an original apple cable but then I was just getting "open XD document" screen.
So I deleted and reinstalled the XD app and then it worked.
So I would make sure:
- you're using an original mac cable
- go to XD app > Settings > Preferences > Remove Offline Docs
- delete and redownload the XD app
- quit desktop app (and maybe even restart comp if convenient)
Hopefull that list works for someone if they have the same issue.