Well with shutterspeeds and frame rates, props can have unpredictable effect frequencies.Ok, you didn't mention that the wind had calmed down. And you mean the frequency of the flicker could match props spinning? I'm having a hard time imagining how the props could interact with the shade in that way.
My review video of the Mavic has a clip at 2:49 that shows a similar effect from the props catching the sun, but it happened to me very infrequently until I got the sunshade:
Hard to tell what exactly is going on, but the fact that it IS going on is what concerns me