Do you use wires in your prototype? Only wired artboards are uploaded, also when navigating via arrows at the bottom or via keyboard.
If you did not wire your artboards then all prototypes should be uploaded. In that case it's a bug and I would be happy to look at your file.
Sorry, what do you mean by wires?
Oh, I see what you mean, they all have to be linked! Got it, yes that answers my question I think. Thanks!
Yes exactly, they all have to be linked.
If you want one with just all artboards then you can upload them without any wires. Then you can click through them with the arrows at the bottom.