Ipad can only hold so much "cached" footage. 2gb I think is the default. You should be pulling the memory card out of the mavic and transferring that footage which is much better quality.
I also had this problem. I could not find a way to fix it. I used a different computer(my laptop) and it worked. I then reformatted and loaded a new windows install and it worked. It must have something to do with windows.