We have found additional cases where an export might fail incorrectly. If you have a project with NO audio in it (all drone footage or all photos for example), it will likely fail to export. Simply add a short audio clip to an audio track (like one of our Logo Stingers from Royalty free music) and you can mute the audio. This will resolve the export issue.
We will have a fix for this issue in 1.4.4.
There can still be "real" export issues caused by certain media with certain edits. This is an ongoing issue that we don't have a simple fix for and continue to investigate. If you have a project that won't export and you have audio in the project, then contact us at firstname.lastname@example.org
and we'll see if we can get your project and resolve the issue.