The biggest road block that our team faced was trying to get more than one interview. The reason why it was a big road block because we didn't know who to interview. We asked a couple of people but some of them said no and it set us back a little bit.
The most important part of the filmmaking process is the interview composition. If the main interview is low quality of there is a technical problem its hard to fix it. The only way to really fix it is to reshot it or add a lot of B-roll.