Same here ... I had several movies rented and they were in my library under rentals, just waiting to be clicked on to play. I updated my iTunes to the new v 188.8.131.52 (updating is always a bad move) and now there are no rentals in my library. Gone... and I still had ten days yet to watch them.
I have this same problem. I tried searching for the movie as pwj19804 suggested and when I typed the name of the movie in my search bar I could see the rental. When I clicked on it, I was taken to the movies section of the library, where the rental still cannot be seen.