I watched the video in the original post with considerable interest, and was quite surprised (and disappointed) to see a glaring issue in the testing procedure that no one has mentioned so far (as of the time of this comment): The "footage" that is compared toward the end of the video is actually a series of still photos taken at UNSYCHRONIZED 2 second intervals during each flight, put together to form a timelapse sequence for each flight. The operator does nothing to synchronize when those photos are taken relative to the start of the mission. Indeed, as you can see throughout the first portion of the video, he initiates the recording of those interval photographs at an apparently random time before the drone reaches waypoint 1 on each flight. This means that photos are likely to be taken at different locations along the flight path on each flight. How much location variability might there be? At 5:02 we see that the global speed for the mission is 10 meters per second. So the distance traveled between each 2 second interval is 20 meters. So, even if the drone followed exactly the same path through space, at exactly the same orientation, there would be no reason to expect the photos to match from flight to flight, and every reason to expect them to NOT match.
The other thing that's a bit mis-guided here is comparing the full paths as shown in Litchi's mission planner, vs the paths traveled by the drone while executing the mission. Yes, the 3 waypoints were created in Litchi, but only those 3 points are being used by the drone while flying. The path that the drone takes to get from one waypoint to the next is being computed by DJI's Waypoint software, not Litchi's. And it is obvious from even casual use of Litchi's mission planner vs DJI's, that the two programs connect waypoints with significantly different path geometries (DJI's are generally more rounded and smoother than Litchi's). So there is no reason to think that the actual path recorded in the DJI flight logs will match the path exported from Litchi, as shown in Google Earth. The only points where you'd expect the paths to match would be at the 3 waypoints.
None of the above takes away from all of the other good and valid comments others make above, regarding reasons why DJI Waypoint missions follow slightly different real world paths each time they run. But the methodology used in preparing this video introduces additional sources of variation that need to be considered when evaluating the results that are presented, and the usefulness of the exercise it documents.