I usually work with 4k or 2.7k video from my gopro and have no problems with this. But yesterday I recorded in 1080p. I edited the footage in adobe premiere elements an exported in 1080p. When I import the footage into VIRB, the footage is scrunched, meaning that it now has horizontal letterboxing. Everything is artificially tall and off. I think it is changing the video from 16:9 to 4:3. Why? How can I fix this? I will post up example footage in a bit. In the meantime you can look at this guy's screenshots. I'm having the exact same problem as this guy: https://forums.garmin.com/forum/mac-windows-software/windows-software/1334085-virb-editor-video-aspect-ratio-changed
When I go to the export page, it only gives me the options to export in 960p, 1440p, and 2.7k. Maybe this information is helpful in understanding what the problem is.
What is the actual resolution of your video? It should only do this if it believes that your video is in fact 4:3, or that 4:3 is the aspect ratio closest to your video's resolution.