My ipad doesn't let me download past movie purchases

I'm having issues when trying to download past movie purchases to my ipad. When I go to the store and purchased tab some of the movies do not show the cloud icon but rather a watch icon. When I click on watch it takes me back tot the movies app which is empty. I have plenty of space and some of the movies do allow for download but more than half don't. Any suggestions? And yes I know I can connect to my computer to download but I want the cloud option when I'm not near my PC.