Mysterious high speed flying object accidentally recorded by drone

This recording shows a very mysterious white object flying directly at and under a small drone that was recording the scenery around Peterborough, Ontario. The day was uneventful. It was sunny and calm with a wind that was barely perceptible. The flight path took the small drone out from the Otonabee riverbank towards a scenic train bridge. The drone operator is directly behind the drone as it begins the flight at 12m (36 feet) above the water. The drone was flying forward at 40km/h (28mph), lifting slowly, recording at 4k, 30fps. The Silver Bean Cafe is behind the drone and the only reason for drone pilot being here this day is to record the scenery around the cafe. Nothing unusual was seen when the recording occurred. But looking through the footage that evening, the owner saw a fast moving object flying through the field of view at the 15 second point in the video. Initially, he thought it was a bird, but this is extremely unlikely because birds do not like the noise of a drone and they will simply not fly so close to one if they can avoid it. Closer analysis shows that the object was visible for less than .5 seconds. Frame by frame inspection shows that it appears and clears the camera view in 15 frames. It is first visible when it dips below the tree line somewhere near the train bridge that is well over 150m (450 feet) away from the drone. A calculation estimates the speed of the object at over 1080km/h (671mph). No bird is able to travel a this speed, especially in a horizontal direction. The slowed down and enlarged footage shows that the object has no wings. It does not look anything like an animal. It is slightly translucent, like plastic and has a different shape than a bird. But litter blowing through the air cannot reach such a speed. It also cannot travel in this manner without extreme wind. A small recreational drone could not remain stable in a gust of wind strong enough to carry this object. A projectile fired from the shore could possibly reach high speeds, but this is too large for a projectile and it is not the correct shape. The object also approaches at a slightly downward trajectory that is too flat for anything that could be launched from shore. The drone shows a small peninsula with houses and a lake beyond. There are no positions high enough to fire at the drone and doing so would have caused the object to strike the cafe behind the drone, or at least the water right in front of the cafe. There is simply no explanation that makes sense enough to explain this high velocity object appearing in this video. Any suggestions or discussion is welcome. But for now, this object is complete mystery.