I have the same problem. Tried all the normal stuff, restarting Apple TV, removing iMovie and reinstalling it, signing out and back in to iCloud, etc, etc, etc. Finally called Apple support but the folks I spoke to, although trying to be helpful and very courteous did not seem to be aware that anyone but me had this problem. Switched to Apple products and software from PCs several years ago because it all just "worked". Support was supposed to call me back but I have not heard from them. Any other ideas on what the deal is with iMovie theater and the missing movies on Apple TV? I have a lot of them that I can see on my phone, iPad and MacBook but not on my big screen TV at the moment.