That is the shadow of the propellers. Did you fly the drone at a high speed with gimbal cover? If so, you can try to remove the gimbal cover and fly at a peaceful speed. See will it help.
Wow, that looks ugly.
Is it there always?
Also when you fly different shutterspeeds (lower preferably)
If it is still there with shutterspeed around 1/60 then the ND filter won't help you.