Had the same issue!!
And turned out to be something very stupid…
The resolution of the camera sensor had a different aspect ration that what I was trying to export (3840 x 2160) Fixed the sensor to Digital film 16:9 and it worked…
I had a similar issue rendering a car scene in the Salt Flats map that Epic provides. What fixed the issue for me was turning off Final Gather Quality under PostProcessVolume > Global Illumination > Lumen Global Illumination