Do you encounter this issue with normal VIRB footage? Does this issue exist before export in VIRB Edit itself, or only once you export a video? We just use the track time to map to a time in the movie, so keeping things synced should be straightforward. I can see a video with an unusual or misreported framerate slowing down the intended playback speed at export, though.
Any chance you could post the original clip video here, too? You can get to that MP4 by right clicking on its thumbnail in the Clip Library and clicking "Show in Finder".
That video is 24 fps. Any non-VIRB video that is not 30 FPS will not sync correctly in VIRB Edit 2.4. The solution PATRIKIOS talks about in this thread is the best way to get that working in VIRB Edit 2.4, but we're going to fix this issue in future versions.