This may be user error, but it seems like when you use branching, all questions after the branching question are hidden until you answer the branching question. It would be better if the full survey was visible, except for any drill-down question, which would just show up in the list based on the response to the branching question.
Office 365 Japan Support Team also filed the same issue.
"I hope for a change in Microsoft Forms branching settings"
I'm having the same issue