48H challenge - Over coming problems

Our 48h challenge film went really well when first started. All our filming went smoothly, the sound was fine and it looked like other footage from the period it was set. Our genre for this film was 'found footage' and we decided to make a film set in WW2 and recreate family footage. We had problems with our sound after editing. When we exported our finished film, it would take a very long time. When it finally finished, the sound was out of sync by 5 seconds. We took out 1 scene and exported that and the sound was completely fine. We then tried exporting the sound and video seperately and putting them back together, but the exported audio only was silent. We then took our out of sync version and lined the sound back up, although we were then missing the last 5 seconds of sound. After waiting an hour for this version to export, it was again silent. We finally had one last go at exporting it before almost giving up on the project. This time we exported the film into 4 parts and then put them together again in a new final cut project. This process finally worked and we were able to solve the problem.
We are hoping that we won't have this problem with future projects, but if we do, we now know to export the film into parts and then put them back together. Our next project (single camera) is being graded on our sound so we are hoping that our solution works again.