When we see something in the sky, our brain is filling in information, that isn't there in reality.
As soon as we film what we see, it will be different than the thing(s) we saw, that is because the camera only does see what we ought to see.
So it isn't always a UFO our eyes are catching, it might be a to earth coming object that fell off a satellite or it's a piece of garbage that's coming down. There's enough in circling around the earth.
That's the same as with the monster of Loch Ness. As soon as somebody does see something different than the water, the brain is filling in the information that the monster is seen, while the camera most of the time does shoot a complete other image.
Try it with objects you know and let other people say to you what they see. You might be surprised in what they tell you.