Thanks, it turns out it was the app automatically desqueezing the footage.
but strangely it was unable to convert to the Cineform GoPro file at this resolution. So I turned off the feature and recaptured in 1080p.
🙁
For now I am setting the project properties to 1920×1080 with par 1.33, and set the “Maintain Aspect Ratio” to false in the pan and cropping tool. Would this be the best way to desqueeze in Sony Vegas Pro?