I also had a simple but easy to make error...
Had planned to take some sunset shots using a graduated ND filter so attached the filter a day in advance, so I would be ready. The next day saw rain in the distance so instead I decided to take a 360 pano. When I saw the result, at first I thought the camera was messed up. But after thinking about it, I realized not to use the graduated ND on 360 panos unless you want to get this result.