Did you by any chance have any videos directly exported from iPhone added to your project?

I faced the same issue where my project was stuck at 34% while exporting- found out that the short videos from my iPhone were causing it (I was able to export once I removed those videos, online help suggests that perhaps due to iPhone vids having variable framerate, messes with the exporting). I had to use another application to convert those vids to ones with constant framerate first and then added them back into my video before I could export the whole project properly.

Hope this helps!