This is just Lens flare & light bloom, find the right combination filter for your lens to get the best result that you like, this is just simple photography & every lens handles direct light down the barrel differently, it is certainly NOT a fault just a common problem when shooting directly into a light source especially the sun as it is one of the strongest source of light there is. Many things will make the flares (or when I charge more for it - Highlights) look better, the height of the UAV, the distance of the sun from the horizon, the position of the sun in frame left right or centre, the shutter setting, the frame rate, the ISO setting, the exposure, the humidity, the filter combination or all, so just work out what makes it acceptable for you as it really is also just personal choice some people love that long colourful light ray effect or as said don't shoot into the sun.