why is imovie no longer working on Ipads?

I use i movie to edit videos I take on my ipad. When I import the movie into ipad it does not play (though you can hear the sound). The top half of the screen is black while the editing lower section passes frames of pics - but not in video form across the screen. I have multiple ipads, all doing the same thing - both before and after the update in August. All worked great for editing video projects in late may and June. Now those video projects no longer play, nor am i able to create new projects. Frustrated as this was always a reliable and easy way to create videos for my students.