@Danieldyrg 

Hi,
For the sake of power saving, the Tapo C420 is usually in a sleep state (low power consumption) when no event is detected. When a motion or movement enters the field of view, the camera will be woken up first and then start to record video, thus the beginning of the motion/movement may not be recorded. The distance between the motion and the camera and the position of the camera may be also related to the issue, for example, if the objects moving directly towards the camera, due to the mechanism of the camera's PIR sensors, it may not be woken up.
You can refer to this FAQ to see how the battery camera/doorbell is woken up.
 

For your issue, would you please help collect the following video recordings and send me a link via private message to download the videos for further analysis?
1) Download the video recordings which has the problem you report.
2) Go to the Live View page of the camera and record the video manually when the same movement occurs.

Best Regards