When exporting a video sequence premiere randomly leaves out part of the audio. Those part were not muted, but in the same channel and of the same kind of other parts exported fine, not even cut: so for instance you have a talker that randomly get the voice silent. This is a big reliability issue, because there is no correspondence of what you have on timeline and what you are going to have on final export. This happens on different machines and happened also with previous versions of Premiere different from this one at moment of writing 15.4.1 (build 4). The only reliably working workaround has been export only the single audio channels in wave files and then import it back into the timeline, that is time consuming and unacceptable for a professional software.