I had the same problem but just tricked the software to pass it. An error message popped out saying something is missing in the mortgage interest section when I finished everything and the software was reviewing the return. I clicked it, nothing was wrong, but then the federal refund turned into a balance owed. I found out that my choice to the same "average loan balance" question got changed and I couldn't save the option "doesn't apply to me". I finally overcame it by choosing "doesn't apply to me" and then "federal review" on the top bar, and the federal refund stayed. So don't click "continue" and jump to the other section if you get stuck in this step.
